I am trying to submit the VAT Return for period to 31/12/20 through solar accounting and the form is requiring HMRC authorisation code which was all done when we sent the first digital return in July 2019. All VAT returns up to period 31/10/2020 went through without this request. What's changed Please ?

Hello Christine,

The authorisation codes that HMRC issue are only valid for 18 months, so
you will need to enter a new HMRC authorisation code from time to time.
Unfortunately this is an HMRC requirement and not something we have control
over.

Thank you for your prompt attention to my question.
I will obtain authorisation code from HMRC.

regards,
Christine Matthews.