are you mainly remote working? it has been a massive benefit in many ways, but one thing it does not support is on the job learning.
clunky systems like this are best taught by having a session like the one you had re procurement, al bit face to face, having instruction notes (i always encourage my team to make their own) and then having a go. if you sat next to someone it is easier to ask questions and observe what they do.
i work in HE admin and find most people pick the systems up this way - and those that struggle need a little bit more support. it's easy to see this when sat in a room together, harder remotely .
for the first month i ask my new starters to come in every day and ensure appropriate team members are in also. after this, dynamic working is phased in.
if you are working remotely, could you ask for this f2f support as part of your pip plan?
btw i have seen a number of pip plans that have been successful - both sides have to approach it in terms of "this gives structure to ensure improvements" - make sure that you feel that the support being offered is going to work.
it's difficult changing career, and admin can be more complex than it seems to get the hang of it, but you will get there. don't be afraid to speak up about the things you struggle with - if you try to hide it you may find that
you end up with a worse situation.