Unable to join Zoom meeting with host key

We have a client that has a H.323/SIP based video endpoint. They are trying to call into a zoom meeting. They are running into an issue with the Zoom host key not working. When they get to the zoom page, they put in the zoom key and get an invalid key error. The client is sure they are putting in the correct zoom key. Do you know if there is anything on the backend of the zoom that needs to be configured or changed?