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TL;DR: I am getting a common error with in app billing, even though I have the correct test accounts. Do I have to opt-in with my test account?

This is my first time with in app billing, and I am getting the following infamous error:

I have read all the documentation a couple of times, and I have added my test accounts in Google Play Console:

On my LG-G3 android device, I have added my test email in the accounts section (so now my phone has two google accounts associated with it)

THE PROBLEM: In the documentation, it says:

Important: To test in-app products or make in-app purchases in your alpha or beta channel app, each tester needs to opt-in to your app’s alpha or beta test. On your test’s opt-in URL, your testers will get an explanation of what it means to be a tester and a link to opt-in.

I believe the reason for my error is because I didn't opt-in with my test account. How do I get that link to opt-in? In the console it says this:

"An opt-in link will be available here when you publish your app." This is odd, because I thought we can test in app billing without publishing to the play store? How can I fix this and get the opt in link?

Thanks,

Ruchir