ISSUE WITH BUY SHIPPING SERVICE

Royal Mail special delivery guaranteed by 1 pm is also not showing up on all my prime orders. It is weird because I was able to use it with my previous One Day Delivery orders (not prime orders). But for my Prime orders, Evri Standard is the only service I can use, and is showing. It is not going to be able to deliver the orders on time, and my delivery performance is getting bad now. Please can somebody help me?