How to use local provider

Hi, I am (very) new to terraform and go. I want to create a provider that talks with a rest-api. I found the Mastercard/restapi example and tried to use that, but it says “Failed to query available provider packages”, because it tries to look at hasicorp/restapi in I have the provider on my computer. Why would terraform look somewhere else? I guess i am missing the logic here.

You might want to try using the one which was published to terraform registry. You can copy/paste the configuration section.

The thing is, this doesnt work for me. I need to make changes to that API, so i cant use this one. I need to find a way to develop locally. Very weird, that this is not documented anywhere. How do other people do it? Publish a blank provider and then edit afterwards?

Docs are there.

I dont think that answers my question of how to develop locally. I checked the docs out a couple of times and i basically got what i want, but terraform wants the provider in the registry and i dont want that. I checked some tutorials of how to do it locally, but they seem to be for an old version which means they dont work anymore.

Ah, indeed I might have misunderstood the brief question.
If you are using terraform 0.14.x you can use these dev_overrides within .terraformrc file.