"we pay" is not correct?
It is correct, yes.
This is a sentence from the Pearson course ( https://www.duolingo.com/comment/24066422 ), and they didn't include "we pay" as an alternative.
Report it as an additional alternative to accept if you'd like.
Is there any singificance between the usages of "zahlen" and "bezahlen"? I assume these are interchangable mostly.
You may find this link helpful https://german.stackexchange.com/questions/7097/when-to-use-bezahlen-and-when-zahlen