If the page was built a while ago and you now have a newer version of DataAssist installed, chances are it will make some updates in the code if you open and re-save the server behavior. Not sure what the significance of the backslash is though, or why it would be added. You could try removing them manually. There certainly doesn't look to be any errors in the code. I see it's a page that runs the insert behavior on page load, so with error reporting on I would expect it to show an error when you load the page if it doesn't write to the database.
Has your server upgraded its PHP version recently? One thing you could try - where single quotes have been used (i.e. ['txn_id']) try changing to double quotes (i.e. ["txn_id"] - I'm not sure if this will make any difference but I've had a few issues when upgrading to PHP8 where I've had to change single to double quotes or vice-versa.
