FBA Small & Light package dimensions not accepted

I’ve been trying to enrol some products to Small & Light but am getting the error message:

‘This product is missing “package dimensions”.’

I’m going around in circles with seller support who have tried to tell me several times that item dimensions are present but package dimensions aren’t. I’ve sent screenshots to prove package dimensions are there (as well as item dimensions) so the latest answer I got is:

‘The Small and Light FBA program is currently not available in your marketplace. We apologize for any inconvenience this has caused.’

I’m reluctant to accept this and haven’t been able to find any information about this anywhere.

Does anyone know if this is true and/or what might be preventing the products from being enrolled on Small & Light?