The normal way to invite people to a CryptPad document is to give them the shared link. No need to register or involve emails. Then, they just need to follow the link and it should just work. CryptPad is specifically designed with nontechnical users in mind, because if you want something to be secure, it needs to be simple, and it is not desirable for privacy to be limited to technical users only.
Sorry I should have been more specific, I was trying to invite a user to a team (can't remember the right terminology) so that they could read and write into a directory, creating as many document as they wanted.
We are a small team of 5, but I'm the only tech-able person, other older users felt extremely disoriented.
Which is frustrating, because to me Cryptpad did everything we needed in a very, very secure way (all encrypted)
What did you want to achieve?