Why not Royal Mail Tracked 48 on buy shipping

Hello apologies for duplication, put it in wrong section

So we have two day shipping eligibility. I am now having trouble getting Royal Mail 48hr Parcel tracked but no problem getting 48hr tracked large letter. Having to do some click and drop outside of the buy shipping API which will soon throw me off 2 day shipping. Pulling my hair out on this. Can not afford to upgrade everything to 24hr which is still an option. Have RM downgraded service level expectations to stop lots of larger parcels overwhelm capacity.

Really need some help here. It might be i simply missed an email or bulletin update

thanks