403 Error when trying to submit VAT return

I'm using 50 Cloud Accounts on a parallels installation on iMac.  I have been using MTD and submitting returns since Sept 2020.  I have come to submit this quarters VAT and I keep getting this error.  The company name and VAT details are correct.  I have contacted HMRC who advised me to delete any permissions for sage on gov.uk and try and reauthorise.  However, the only option I get when trying to proceed is 'continue' and this only returns this error.  There is only one user (me) and I have full control.  Any ideas?