Breakdown of entairyoukin ga aru.

Questions & Answers about entairyoukin ga aru.
が marks 延滞料金 as the thing that exists.
With ある, Japanese often uses the pattern:
[thing] が ある = there is [thing] / [thing] exists
So:
延滞料金がある
= There is a late fee / A late fee exists
This is different from English, where we often use there is as a dummy subject. In Japanese, the actual thing being talked about is marked directly with が.