SFP Impossible with Royal Mail How do I get DPD added as a courier in Buy Shipping?

OK so I am STILL trying to get through the SFP trial period and have come to the conclusion that it is impossible if using Royal Mail as the 24 tracked service doesn’t have a high enough success rate of getting parcels there on time. I’m not sure how it is my fault if Amazon offer this as a service for SFP and it doesn’t perform. Anyway, the only alternative I have it DPD so I need to get that added to buy shipping so I can do the trial label thingy - I’ve been looking through the help section this morning but can’t find out how to do this, can anyone advise please?