Buy Shipping shows Amazon Onboarding

Since last week my seller fulfilled prime orders have shown that I need to onboard to Amazon in order to 'Buy Shipping' even though I've been onboard with DPD for several years. At some point, the order will then miraculously revert to the standard delivery options allowing me to pay for postage and despatch the parcel within the SLA.

I've raised this with support and sent numerous screen shots only to find that they insist I onboard and then close the case, so I open a new one and the games goes on.

Anyone else struggling with this?