Making Tax Digital

Can anyone help me with the below error message?

I used to click a button in the same place as this one, and it would let me submit my own VAT returns. Now, I can't do it and had to ask my Accountant to submit it for me.

When I click the "Take Action" button, I'm taken to the next screenshot and I can't get make any sense of it. I've underlined an "Error Code" at the bottom "CLIENT_OR_AGENT_NOT_AUTHORISED"

Any ideas?

Thank you