Ive had the same problem,
I can fill out the form but ‘Next’ button does nothing,
On the previous screen i see an empty mandatory field that is greyed out so i cant even manually enter it (its phone number if anyone curious).

Exactly that for me.

I raised a phone support call for one issue and advised I was unable to raise online ……… they said they were aware of that, but nothing seems to have changed.

We apologize for the inconvenience. Our engineers are actively working to resolve the issue with submitting a Support case on the RingCentral website. Thank you for your patience as we work to fix this as quickly as possible.