Making the app default messaging app will prevent the storage of both sent and received messages so make sure you have the “Read Received” option turned on so you can see the received messages in the SMS Gateway app.

Unset app as the default app

If you won’t revert the above changes then you can open your primary messaging app and it will prompt you to make it a default app. Just choose “Yes” and you will be able to store sent and received messages in your primary messaging app.