Buffer has deprecated their API and no longer supports it. Therefore I do not recommend using the Buffer integration as it may break any time.
According to this article, you can use a similar product called Ayrshare, however this external service doesn’t have an integration on Make yet.
Ayrshare has a Developer API Reference/Documentation, which you should be able to integrate the endpoints in Make using the generic HTTP module.
You can also suggest for it to be made in the Idea exchange. Don’t forget to search for it first, just in case someone already suggested it, so that you don’t end up creating a duplicate.
You can get a Ayrshare API key here https://app.ayrshare.com/api for use with the HTTP “Make an API key request” module.
If you need assistance in setting up the generic HTTP module to call this external service, please start a new thread, providing information about what you have tried with regards to the external service’s Developer API Reference – how you are setting the connection up, a link to the endpoint are you trying to connect to, and what errors you are encountering.