move attachment info to submit-support-request.md

Author: ThijsSeppen

content/en/docs/support/submit-support-request.md

@@ -132,6 +132,14 @@ You can add large attachments such as app files to the request. Please note that
 Attachments added to Mendix Support requests will be automatically deleted after 365 days.
 {{% /alert %}}
 
+Attachments are uploaded via SendSafely, a secure file transfer service. SendSafely may be blocked by your network, which prevents the widget from displaying. In that case, the page shows a `Could not render widget 'SupportPortal.SendSafely.sendSafelyDropzone1'` error. 
+
+To resolve that error, please make sure that the following URLs are allowlisted in your network's security settings:
+
+- `https://mendix.sendsafely.eu`
+- `https://static-mendix.sendsafely.eu`
+- `https://sendsafely-dual-region-eu.s3-accelerate.amazonaws.com`
+
 ### Logs
 
 It is important to provide app logs when submitting a support request. This allows the support team to better assess and work towards fixing the issue. The following sections include information on retrieving logs per deployment model.