Getting bearer token/API credentials

Receved API keys last december but finally have time to actually start the project.
Is it possible the keys expired because whatever I do, I get “invalid_grant” error.

I followed various examples, which are all basically the same. It’s like nails on chalkboard seeing “Content-Type” set to “application/json” when the content is always www-form-encoded. Also, the docs read “you need these 3 things” and then only list 2 things but mention Access Token a lot, which I think is legacy/irrelevant now. e-mail that included the API keys said to come here if there was any issue.

But, fine, I tried postman and curl and talend api tester. My only conclusion is my keys aren’t valid.