"Pop for" is a colloquial expression that means "to pay for something, especially for someone else's benefit". There are several synonyms that can be used instead of "pop for". For example, you can say "pick up the tab" or "foot the bill" to mean the same thing. Another colloquial expression that can be used as a synonym for "pop for" is "spring for". Additionally, you can simply say "buy" or "purchase" to refer to the act of paying for something. Regardless of which synonym you choose to use, the meaning and intent of the original phrase remain the same.