This would normally indicate that the VAT registration number held inside your Sage 200 application is incorrect, however, if this is confirmed to be correct then the likelihood is that the option to Submit as a digital record as part of Making Tax Digital has not been enabled.
For Sage 200 Standard, you can check this by going to Settings, Cash Book / Nominal Ledger then into the Nominal Ledger Settings. The tick box is on the VAT Submissions tab.
For Sage 200 Professional, go to Nominal Ledger, Utilities, Ledger-Set Up then Ledger Settings. As above, the tick box is on the VAT Submissions tab.