I'm having trouble showing an ad using API

If you use implicit you’ll get a #access_token=asdasdasd
if you use Authorization Code flow you’ll get a ?code=asdasd and you exchange the ?code for an access and refresh token

For your use case you generally would not use OIDC

You would generally use oAuth Authorization Code Grant Flow to get a refresh token so you don’t need to get a new token periodicially.

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