Invoice from one academic or another? (3-5)

'invoice' is the definition.
(I've seen this before)

'from one academic or another?' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'from' is 'form' which is located in the answer.
'one' could be 'a' (a thing is one thing) and 'a' is located in the answer.
'another?' could be 'r' (I've seen this in other clues) and 'r' is present in the answer.
The remaining letters 'po' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

Can you help me to learn more?