You cannot register at the moment, this may change in the future. If you already are registered, you can additionally login to Mattermost with this account. Please note that once the migration to Matrix has finished, the Mattermost server will reach end of service.
If you managed to piss me off so badly that I blocked you, all your requests will be answered with HTTP status 402 "Payment required". Despite the wording, throwing cash at me will not change my position.