Is the Mojang API deprecated?

Hi, I've been coding with C# and using the Mojang API for various tasks such as obtaining user UUIDs which works great, but every time I do a POST request to change my name is gives me a 403 with this error:

{ "error": "ForbiddenOperationException", "errorMessage": "Route no longer supported." }

There is no apparent documentation in the API explaining this error, so I'm wondering why this is happening. Earlier I was only returning the status code so I thought like I was going crazy. Any news on a new API or solution for this issue?

 

Thanks,

 

Luca.