I’m not very familiar with coding, and I’m at the last step to be able to send messages from my WhatsApp account and phone number. I need to register the number using a certificate first.
However, when I click on the instructions from Facebook, which should explain the process, the page shows an error.
Could someone help me register this number?
Welcome to the Postman Community! 
I have never used that API before so I wouldn’t know much more that what you can see in the documentation. It looks like a big red warning telling you that the route is being sunsetted so that’s likely not going to work anymore. 
I don’t know if there is an alternative endpoint that can be used - It might be worth posting this question of on a Meta specific forum to get some context from them.
But have you never entered a certificate to register a number? Because I need to do something like that, and I have no idea how.
When I click on “these instructions,” the page that appears is the one I initially sent in my first message.
I’ve never used that API and never needed too so I’ve never entered a certificate to register a number before.
As I mentioned before, this is very much a usage based question that should be directly asked to the Meta/WhatsApp team - I’m sure that they will have their own Community where the experts in that particular topic will be able to assist you.
