diff --git a/api/v3/filters/parse.go b/api/v3/filters/parse.go
index 8b437da1f5..cbd6821b8a 100644
--- a/api/v3/filters/parse.go
+++ b/api/v3/filters/parse.go
@@ -161,12 +161,25 @@ func parseFiltersValue(qs url.Values, v reflect.Value) error {
 			fieldVal.Set(reflect.ValueOf(&parsed))
 
 		case stringPtrType:
+			if hasOperatorStyleKeys(qs, name) {
+				return fmt.Errorf("filter[%s]: operator-style keys are not supported for this field", name)
+			}
 			if err := parseStringPtr(qs, name, fieldVal); err != nil {
 				return err
 			}
 
 		default:
-			return fmt.Errorf("filter[%s]: unsupported filter field type %s", name, fieldVal.Type())
+			// Handle *T where T is a named string-based type (e.g. *BillingCreditTransactionType).
+			if fieldVal.Kind() == reflect.Pointer && fieldVal.Type().Elem().Kind() == reflect.String {
+				if hasOperatorStyleKeys(qs, name) {
+					return fmt.Errorf("filter[%s]: operator-style keys are not supported for this field", name)
+				}
+				if err := parseStringPtrTyped(qs, name, fieldVal); err != nil {
+					return err
+				}
+			} else {
+				return fmt.Errorf("filter[%s]: unsupported filter field type %s", name, fieldVal.Type())
+			}
 		}
 	}
 
@@ -192,6 +205,27 @@ func parseStringPtr(qs url.Values, name string, fieldVal reflect.Value) error {
 	return nil
 }
 
+// parseStringPtrTyped handles filter[field]=value for *T fields where T is a named string type.
+func parseStringPtrTyped(qs url.Values, name string, fieldVal reflect.Value) error {
+	prefix := "filter[" + name + "]"
+	for key, values := range qs {
+		if key != prefix {
+			continue
+		}
+		val, err := singleValue(key, values)
+		if err != nil {
+			return err
+		}
+		if val != "" {
+			ptr := reflect.New(fieldVal.Type().Elem())
+			ptr.Elem().SetString(val)
+			fieldVal.Set(ptr)
+		}
+		break
+	}
+	return nil
+}
+
 // parseFilterString extracts a FilterString supporting all string operators.
 func parseFilterString(qs url.Values, field string) (FilterString, error) {
 	var f FilterString
@@ -502,6 +536,17 @@ func hasFilterKeys(qs url.Values) bool {
 	return false
 }
 
+// hasOperatorStyleKeys reports whether qs contains any filter[field][op] keys for the given field.
+func hasOperatorStyleKeys(qs url.Values, name string) bool {
+	prefix := "filter[" + name + "]["
+	for key := range qs {
+		if strings.HasPrefix(key, prefix) {
+			return true
+		}
+	}
+	return false
+}
+
 // hasFieldKeys reports whether qs contains filter[field] or filter[field][op] keys.
 func hasFieldKeys(qs url.Values, field string) bool {
 	prefix := "filter[" + field + "]"
diff --git a/api/v3/filters/parse_test.go b/api/v3/filters/parse_test.go
index dcb42b95e9..8cf491fe39 100644
--- a/api/v3/filters/parse_test.go
+++ b/api/v3/filters/parse_test.go
@@ -13,6 +13,8 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+type testStringType string
+
 // testFilter is a target exercising every filter type Parse recognizes.
 type testFilter struct {
 	Field     *FilterString      `json:"field,omitempty"`
@@ -24,6 +26,7 @@ type testFilter struct {
 	CreatedAt *FilterDateTime    `json:"created_at,omitempty"`
 	Enabled   *FilterBoolean     `json:"enabled,omitempty"`
 	Currency  *string            `json:"currency,omitempty"`
+	TxType    *testStringType    `json:"tx_type,omitempty"`
 }
 
 func TestParse_FilterString(t *testing.T) {
@@ -301,6 +304,37 @@ func TestParse_StringPtr(t *testing.T) {
 	})
 }
 
+func TestParse_NamedStringType(t *testing.T) {
+	t.Run("named string type filter value", func(t *testing.T) {
+		var f testFilter
+		require.NoError(t, Parse(url.Values{"filter[tx_type]": {"funded"}}, &f))
+		require.NotNil(t, f.TxType)
+		assert.Equal(t, testStringType("funded"), *f.TxType)
+	})
+
+	t.Run("nil when no filter key present", func(t *testing.T) {
+		var f testFilter
+		require.NoError(t, Parse(url.Values{}, &f))
+		assert.Nil(t, f.TxType)
+	})
+
+	t.Run("operator-style key rejected", func(t *testing.T) {
+		var f testFilter
+		err := Parse(url.Values{"filter[tx_type][eq]": {"funded"}}, &f)
+		require.Error(t, err)
+		assert.Contains(t, err.Error(), "operator-style keys are not supported")
+	})
+}
+
+func TestParse_StringPtrOperatorRejected(t *testing.T) {
+	t.Run("operator-style key rejected for *string field", func(t *testing.T) {
+		var f testFilter
+		err := Parse(url.Values{"filter[currency][eq]": {"USD"}}, &f)
+		require.Error(t, err)
+		assert.Contains(t, err.Error(), "operator-style keys are not supported")
+	})
+}
+
 func TestParse_PointerToPointer(t *testing.T) {
 	t.Run("allocates pointer when filter keys exist", func(t *testing.T) {
 		var f *testFilter