I had one left over and didn’t know where to use it so I dropped it in there as in those visa’s (as in being possessive) belonged to the people who applied for them.
The apostrophe indicates possession by the article.
For example:
"The window's latch is broken.'
The latch belongs to the article (the window).
If the visas belong to the people, they're the people's visas.
Convert the word 'visa' to the possessive case:
'The visa's stamps are incorrect.'
'The visa's owner has not showed up to claim it.'