You may have been opted into Simple Delivery which, currently you can opt out, but from the 15th April it will become mandatory for all Private Sellers.
For the time being try this:
Simple Delivery is not compulsory..... yet, so you can opt out if you wish. I believe you'll need a laptop / PC and use Chrome for this, maybe not the app or mobile browser.
When creating a new listing here's how to opt out:
Click on Collection then straight away back to and click on Postage Only, and the Custom option shows, you are then able to select the postage service and cost you wish to use.
Or, if there is a switch link, click on ' Switch to Advanced Options' at the bottom of the postage section, and once again when a pop up appears.
This explains Simple Delivery which as said will be mandatory from the 15th April for Private sellers.
https://www.ebay.co.uk/sellercentre/postage/simple-delivery?mkevt=1&mkpid=2&emsid=0&mkcid=8&bu=43952...
