Hey there @DeborahLevyBen,
Sometimes, an "Internal Server Error" (500) can occur due to server overload, or when the data being transmitted is too large, or a host of other circumstances. More about errors here: https://help.zapier.com/hc/en-us/articles/8496037690637-Troubleshoot-errors-in-Zapier
As this issue occurs on the other app's end, it's tough to determine the exact problem. However, the good news is that such issues usually don't last long. Once they subside, failed tasks can be replayed in bulk from the Task History.
For more information on replaying tasks, I suggest checking out this help document: https://zapier.com/help/manage/tasks/replay-failed-tasks-in-zaps.
Hopefully, this helps!