Hello there,
I tried to look through the forums to see if there was something that matched my issue to save time, but I was unable to find anything.
I am trying to receive and post invoice on the PO, and my no series is filled out for everything:

I am using a value from the Vendor's proforma invoice, and am unsure if that is causing the issue as it does not match the no series nomenclature? I have a pre-payment invoice on this PO as well, and then add a "-B" when posting the invoice so that there is a way to differentiate between.
Thank you enormously in advance for the support! :)
Shaun