It sounds frustrating to deal with issues like this. Here are a few steps you can try to resolve the problem with Google Pay on your iPhone 15 Plus:
1. **Ensure Latest App Version**: Make sure you have the latest version of the Google Pay app installed. Sometimes, bugs are fixed in newer updates.
2. **Check iOS Version**: Ensure your iPhone is running the latest version of iOS. Go to Settings > General > Software Update to check for updates.
3. **Google Pay Settings**:
- Open the Google Pay app.
- Go to Settings and ensure all required permissions are granted, especially for contacts, location, and network access.
4. **Clear Cache (if applicable)**:
- Although iOS doesn't have a direct way to clear app cache, you can try deleting the app and reinstalling it. This can help clear any temporary issues.
5. **Re-verify Bank Details**:
- Double-check the bank details you are entering. Ensure they match exactly with your bank's records.
6. **SIM and Network Settings**:
- Since you have already tried both eSIM and physical SIM, make sure your network settings are correctly configured. Sometimes, a manual carrier update might be needed.
7. **UPI Issues**:
- Ensure your bank supports UPI on iPhones. There might be specific compatibility issues with certain banks.
8. **Regional Settings**:
- Check if the regional settings on your iPhone are set correctly for India. Sometimes, incorrect regional settings can cause issues with UPI.
9. **Contact Google Pay Support**:
- If none of the above steps work, it might be best to contact Google Pay support directly. They can provide specific guidance and check if there's a known issue with iPhone 15 Plus.
10. **Bank Support**:
- Sometimes, the issue might be on the bank's side. Contact your bank's customer support to ensure there are no issues with your UPI ID or account.
Since you have already tried resetting network settings and phone settings, the issue might be more specific to software compatibility or configurations. If these steps do not resolve the issue, providing detailed feedback to Google Pay support might help them identify and address the problem more effectively.