Currently, we have an on-going issue where users, like you, are unable to submit your BAS with an error message saying An application error has occurred while processing your request.
Rest assured that we've already informed our engineering team about this and they're diligently working in all hand s to fix this as soon as possible.
In the meantime, you may want to consider manually submitting your BAS directly from the Australian Taxation Office Business Portal page. This way, you can avoid submitting your BAS with late fees or penalties.
In addition, I'd recommend contacting our Customer Care Support so you'll be added to the list of affected users. Once added, you'll receive all available updates about this investigation through your email. To do so: