I have been trying to submit my own Tax Return for days now using HMRC online system not commerical software, but every time I hit the submit button. I get this error message:
"Hmm. We’re having trouble finding that site. We can’t connect to the server at citizen-auth-frontend.public.mdtp." That's using the firefox browser
I've tried using microscoft browser and get a similar message.
This site https://downdetector.co.uk/status/hmrc/ indicates there are reported problems with HMRC website.
The only advice from HMRC is to "clear cache" and try again later.