Hi there!
1. The PHP client library does not allow unknown parameters to be passed, I'm afraid. The workaround for this is
a. You can change the callback URL on our side, although it's a manual process and can take a couple of weeks.
b. Look for class Google_AssociationsessionsServiceResource and add 'callbackUrl' to the start function as a parameter.
2. and 3. What do you mean with "gave access"? Associated? You have to authenticate with your host account (arslan.tune) and only use the publisher account for the association flow. You will never have to use OAuth2 with your publisher account. I'd recommend you to create new accounts when associating with the sandbox host, not to use existing ones.
4. You can check that with the associationsession.verify method.
5. Sandbox accounts do not show ads.
Cheers,
Jose
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Jose Alcérreca
Developer Relations
Google UK Limited
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