Thanks for reaching out. An Error 403 when registering for a Zoom meeting generally indicates that access to the registration page or request is being denied.
A few things you can try first:
Open the registration link in a private/incognito browser window.
Try a different browser or device.
Clear your browser cache and cookies.
If you're accessing the registration link through a company or school network, try a different network if possible.
Make sure you're using the most recent registration link provided by the meeting host.
If you're still receiving the 403 error after trying these steps, I recommend submitting a ticket to Zoom Support so they can review the specific registration error and account/meeting configuration.
If you can provide the meeting registration link, the email address being used to register, and a screenshot of the error, Support should be able to investigate further.