Registration error

We've created a webinar using zoom and after trying several times for registration, we've found that we sometimes face the issue below when to try registration via form.

Error
Post Registration time-out, Please try again latter
500 - v=2.0;clid=aw1;rid=INT_2a9abe19ccb94e27

Additional info

- We use pardot form to let the participants to enter their info and put the zoom webinar registration link in the thanks mail.

- We also intergrate with Pardot for registration, attendee and absentee list.

What I'd like to know

- How to solve this issue

- What are the possible reasons that this error occurs.