Buy Shipping Code for MWS

[Packitsafe]

Hi,

Does anyone know the code you have to use to buy shipping via MWS on amazon seller central for the new Royal Mail 48 (Large Letter) (CRL), we have tried ROYAL_MAIL_RM48_SC_LL-0 but does not work. But shows in Seller Central and we can buy on there but not via API.

Or is that need authorising somewhere else.

Any Help would be helpful.

Many Thanks