Oh the fun of VAT. Dynamics Explorer digs into a VAT issue.
I had a client report this issue recently which was preventing them submitting the VAT return to HMRC via the government gateway. The exact error is below After some digging it seems the period key is passed down from HMRC when the obligations are retrieved therefore its strange that the error is produced when submitting…
— Read on thedynamicsexplorer.com/2019/09/25/dynamics-gp-error-message-period_key_invalid-when-submitting-vat-return-to-hmrc/