[iOS] requestPurchase throws 'incorrect format' error with withOffer

[jeonghyerin1]

Description

When calling requestPurchase from the useIAP hook with the withOffer property included, the request fails with the following error:

[RnIap] requestPurchase failed: 올바른 포맷이 아니기 때문에 해당 데이터를 읽을 수 없습니다.

[translation]

[RnIap] requestPurchase failed: The data couldn’t be read because it isn’t in the correct format.

---

Describe the solution you'd like

I would like the functionality of requestPurchase with the withOffer property to be restored to how it worked in version 12.16.2.

The ideal solution would be to re-investigate the fix from issue #2715 (specifically the changes mentioned in this comment) and apply a similar, permanent fix to version 14.4.15 and future releases.

---

Additional Context

While I was using version 12.16.2, I encountered a similar problem described in issue #2715. I was able to fix it by applying a patch based on the solution in this comment.

After upgrading to 14.4.15, this patch was removed, and the error has returned.

---

Enviorment

• react-native-iap: 14.4.15
• react-native: 0.80.1
• Platforms: iOS

[hyochan]

Hi @jeonghyerin1,

I've investigated this issue and found the root cause.

Your backend server is not base64-encoding the signature. The OpenIAP library requires promotional offer signatures to be base64 encoded:

OpenIAP Code (StoreKitTypesBridge.swift:404-407):

guard let signature = Data(base64Encoded: offer.signature) else {
    OpenIapLog.error("❌ Invalid signature format (must be base64): \(offer.signature)")
    return nil
}

When the signature is not base64, this guard fails and returns nil, causing the error you see.

This is NOT a bug in react-native-iap

The issue from #2715 was already fixed in OpenIAP 1.2.13. Your version (react-native-iap 14.4.15) uses OpenIAP 1.2.18, which includes the fix.

Solution 🛠️

Update your backend to base64-encode the signature:

Before (❌ Wrong):

const signature = sign.sign(privateKey);
return { signature: signature.toString('hex') }; // Wrong!

After (✅ Correct):

const signature = sign.sign(privateKey);
const base64Signature = signature.toString('base64'); // Required!
return { signature: base64Signature };

Complete Example (Node.js)

const crypto = require('crypto');
const { v4: uuidv4 } = require('uuid');

function generatePromotionalOfferSignature(productId, offerId, applicationUsername, privateKey, keyId) {
  const nonce = uuidv4();
  const timestamp = Date.now();

  const dataToSign = [
    applicationUsername,
    offerId,
    productId,
    nonce.toLowerCase(),
    timestamp.toString()
  ].join('\u2063');

  const sign = crypto.createSign('sha256');
  sign.update(dataToSign);
  const signatureBuffer = sign.sign({ key: privateKey, format: 'pem', type: 'pkcs8' });

  // ⭐ This is the critical part
  const base64Signature = signatureBuffer.toString('base64');

  return {
    identifier: offerId,
    keyIdentifier: keyId,
    nonce: nonce,
    signature: base64Signature, // Must be base64!
    timestamp: timestamp
  };
}

Debugging 🐛

Check Xcode console. If you see this error, your signature is not base64:

❌ Invalid signature format (must be base64): [your_signature]

References 📚

• Apple: Generating a Signature for Promotional Offers
• Apple: Sample Server Code

Both Apple's documentation and sample code show that the server should return a base64-encoded signature.

---

TL;DR: This is a backend issue, not a react-native-iap bug. Base64-encode your signature on the server.

[jeonghyerin1]

@hyochan Thank you for your reply!

I can confirm that the signature generated by our server is indeed in Base64 format. Also, I am not seeing the ❌ Invalid signature format (must be base64): [your_signature] log in the Xcode console.

The only error that consistently appears is this one:

[RnIap] requestPurchase failed: 올바른 포맷이 아니기 때문에 해당 데이터를 읽을 수 없습니다.

After reviewing our server implementation, it seems the signature generation part differs from what is described in the Apple documentation and your example.

I was wondering if this could be related to the issue?
(Just to add, I did try implementing the signature generation exactly like your example, but unfortunately, the same error still occurs.)

Apple documentation

appBundleId + '\u2063' + keyIdentifier + '\u2063' + productIdentifier + '\u2063' + offerIdentifier + '\u2063' + appAccountToken + '\u2063' + nonce + '\u2063' + timestamp

Our implementation

payload := strings.Join([]string{
		s.cfg.Apple.Subscription.BundleID, // app bundle id
		s.cfg.Apple.Subscription.KeyID, // key id
		string(request.SubscriptionProductID), // product id
		request.OfferID, // offer id
		result.AccountSubscriptionToken, // app account token
		nonce, // nonce
		strconv.FormatInt(timestamp, 10), // timestamp
	}, "\u2063")

Your example

  const dataToSign = [
    applicationUsername,
    offerId,
    productId,
    nonce.toLowerCase(),
    timestamp.toString()
  ].join('\u2063');

[hyochan]

Hi @jeonghyerin1,

I apologize for my incomplete response earlier - I was reviewing this late and missed some important details.

After looking at your Go implementation more carefully, I realize your data order is actually correct. The issue in my previous example was incomplete.

Updated Documentation

I've just updated our documentation with a complete server-side signature generation guide:

📚 Subscription Offers - Server-Side Signature Generation

The documentation now includes:

1. Complete Node.js example with all 7 required fields in the correct order
2. Important notes about nonce (lowercase), timestamp (milliseconds), and base64 encoding
3. Common error messages and their causes

Your Go Implementation Check

Your implementation has the correct order:

payload := strings.Join([]string{
    s.cfg.Apple.Subscription.BundleID,      // ✅ 1. bundleId
    s.cfg.Apple.Subscription.KeyID,          // ✅ 2. keyId
    string(request.SubscriptionProductID),   // ✅ 3. productId
    request.OfferID,                         // ✅ 4. offerId
    result.AccountSubscriptionToken,         // ✅ 5. appAccountToken
    nonce,                                   // ✅ 6. nonce
    strconv.FormatInt(timestamp, 10),        // ✅ 7. timestamp
}, "\u2063")

Since your order is correct, please verify these additional points:

Checklist

1. Nonce format:

   nonce := strings.ToLower(uuid.New().String()) // Must be lowercase

2. Timestamp (milliseconds, not seconds):

   timestamp := time.Now().UnixNano() / int64(time.Millisecond)

3. Signature encoding (must be base64):

   signature := base64.StdEncoding.EncodeToString(signatureBytes)
   // NOT hex.EncodeToString()

4. Private key format (PKCS#8 PEM):

   block, _ := pem.Decode([]byte(privateKeyPEM))
   privateKey, err := x509.ParsePKCS8PrivateKey(block.Bytes)

If you're still seeing the "incorrect format" error after verifying these points, could you share (without sensitive data):

• How you're encoding the signature (base64/hex)?
• The timestamp format you're using?
• Whether the nonce is lowercase?

Sorry again for the confusion in my initial response. The updated documentation should help clarify the complete implementation.

[jeonghyerin1]

@hyochan Thank you for the checklist. I have reviewed all the points and it seems that everything is applied correctly on our end. However, as I'm still consistently encountering the "incorrect format" error, I am providing the information below.

• How you're encoding the signature (base64/hex)?
  • Please refer to the code below.
• The timestamp format you're using?
  • milliseconds (time.Now().UnixMilli() -> string)
• Whether the nonce is lowercase?
  • The nonce was not converted to lowercase. However, I suspect this isn't the issue because the generated UUID is already entirely in lowercase.

// GetAppleSignatureForOffer 애플 오퍼를 위한 서명 생성
// 애플 공식 문서: https://developer.apple.com/documentation/storekit/generating-a-signature-for-promotional-offers
func (s subscriptionUsecase) GetAppleSignatureForOffer(ctx context.Context, request domain.GetAppleSignatureForOfferRequest) (domain.GetAppleSignatureForOfferResponse, error) {
	// 1. 필요한 값들 준비
	result, err := s.subscriptionHelper.CreateUserAccountToken(ctx, domain.CreateUserAccountTokenArgs{
		UserID:       request.CurrentUserID,
		PlatformType: lo.ToPtr(mc.PaymentPlatformTypeAppleAppStore),
	})
	if err != nil {
		return domain.GetAppleSignatureForOfferResponse{}, err
	}

	// 2. nonce와 timestamp 생성
	nonce := uuid2.New().String()
	timestamp := time.Now().UnixMilli()

	// 3. payload 생성 (invisible separator 문자 사용)
	payload := strings.Join([]string{
		s.cfg.Apple.Subscription.BundleID,
		s.cfg.Apple.Subscription.KeyID,
		string(request.SubscriptionProductID),
		request.OfferID,
		result.AccountSubscriptionToken,
		nonce,
		strconv.FormatInt(timestamp, 10), // string로 변환
	}, "\u2063")

	// 4. 개인키 파싱
	block, _ := pem.Decode([]byte(s.cfg.Apple.Subscription.KeyContent))
	if block == nil {
		return domain.GetAppleSignatureForOfferResponse{}, eu.InternalError(fmt.Errorf("failed to parse PEM block containing the private key"))
	}

	privateKey, err := x509.ParsePKCS8PrivateKey(block.Bytes)
	if err != nil {
		return domain.GetAppleSignatureForOfferResponse{}, eu.InternalError(fmt.Errorf("failed to parse EC private key: %v", err))
	}

	// 5. payload 해시
	hasher := sha256.New()
	hasher.Write([]byte(payload))
	hash := hasher.Sum(nil)

	// 6. 서명 생성 (DER 형식으로)
	ecdsaPrivKey, ok := privateKey.(*ecdsa.PrivateKey)
	if !ok {
		return domain.GetAppleSignatureForOfferResponse{}, eu.InternalError(fmt.Errorf("private key is not an ECDSA key"))
	}

	// DER 형식의 서명 직접 생성
	signature, err := ecdsa.SignASN1(rand.Reader, ecdsaPrivKey, hash)
	if err != nil {
		return domain.GetAppleSignatureForOfferResponse{}, eu.InternalError(fmt.Errorf("failed to sign payload: %v", err))
	}

	// 7. 서명 인코딩 (Base64)
	signatureBase64 := base64.StdEncoding.EncodeToString(signature)

	return domain.GetAppleSignatureForOfferResponse{
		KeyIdentifier: s.cfg.Apple.Subscription.KeyID,
		Signature:     signatureBase64,
		Nonce:         nonce,
		Timestamp:     timestamp,
	}, nil
}

using uuid2 "github.com/google/uuid"

[hyochan]

After reviewing your code and researching similar issues, I found what's most likely causing the problem.

Most Likely Issue: appAccountToken Case Sensitivity

Based on a critical bug fix in RevenueCat's StoreKit 2 implementation, the appAccountToken MUST be lowercase.

From Apple's documentation:

"Use lowercase for the string representation of appAccountToken."

Your current code:

payload := strings.Join([]string{
    s.cfg.Apple.Subscription.BundleID,
    s.cfg.Apple.Subscription.KeyID,
    string(request.SubscriptionProductID),
    request.OfferID,
    result.AccountSubscriptionToken,  // ← Is this lowercase?
    nonce,
    strconv.FormatInt(timestamp, 10),
}, "\u2063")

Suggested Fix

Try adding explicit lowercase conversion:

payload := strings.Join([]string{
    s.cfg.Apple.Subscription.BundleID,
    s.cfg.Apple.Subscription.KeyID,
    string(request.SubscriptionProductID),
    request.OfferID,
    strings.ToLower(result.AccountSubscriptionToken), // ⭐ Add this
    strings.ToLower(nonce),                            // ⭐ And this (just to be safe)
    strconv.FormatInt(timestamp, 10),
}, "\u2063")

Additional Resources

Key references:

• RevenueCat StoreKit 2 Fix #2114
• Updated Documentation

If This Doesn't Work

If the lowercase fix doesn't resolve it, please check:

1. Environment key: Are you using the test key for StoreKit Testing (not production key)?
2. Private key format: Verify it's PKCS#8 PEM format
3. Xcode console logs: Any additional error messages beyond "incorrect format"?

I'm fairly confident the lowercase conversion will fix it, as this was the exact issue that caused similar errors in production for other developers. Please let me know how it goes!

[jeonghyerin1]

@hyochan

The appAccountToken also uses a Google UUID, so it consists entirely of lowercase letters (although I'm not explicitly converting it to lowercase).

• Environment key: Are you using the test key for StoreKit Testing (not production key)?
  • I didn't quite get that. Could you please explain it in more detail?
• Private key format: Verify it's PKCS#8 PEM format
  • yes
• Xcode console logs: Any additional error messages beyond "incorrect format"?
  • There were no other error messages except for "incorrect format."

[hyochan]

@jeonghyerin1 I took a short nap and looked at this again with a clearer head. It seems this fix might address the “incorrect format” error you’ve been seeing. From what I can tell, your backend signature generation looks correct — the issue likely lies in how react-native-iap was passing the promotional offer data to the underlying StoreKit 2 layer.

When this is released hyodotdev/openiap-apple#26, I think it may resolve the type cast issue.

[hyochan]

@jeonghyerin1 Please test 14.4.19 and let me know 🙏

[jeonghyerin1]

It works Thank you!!! 감사합니다~~