Hey Mia,
sorry but who gave you this information? That’s absolutely not how you create a Pinterest connection in Make.
All you need on Make side is App ID and App Secret Key of your Pinterest app.
And then on Pinterest side you just need the proper make.com redirect URI.
That’s it. You don’t need to handle token exchanges or make these custom HTTP calls, those are done by Make in the background.
And before you get stuck on the next step, you can read more here on how to create video pins.