This is version 3 of Registration API. Check this link to see sample data and scenarios to use RegistrationAPI.  The hostname for YBS and Chelsea brand is ob-ybs.sandbox.ybs.co.uk and ob-che.sandbox.ybs.co.uk respectively.Swagger specification link is here.

Client Registration

Method
Description

POST

ClientRegistration

https://hostname/open-banking/v1.0/register/tpp-client

Endpoint will be secured by way of Mutual Authentication over TLS