Interesting. Maybe there are other things that can cause this too, but several people here are reporting that they're unable to login to Defender for Android (with any account, child or otherwise) on an Android device managed by Google Family Link. I believe this is different than the login issue that was happening earlier in July that Sumit mentioned was resolved. Keep in mind we're not getting a notice that we need to purchase a M365 subscription, we're getting a small error message saying, "Invalid license, please contact administrator". See screenshot in the original post above. Definitely a device issue as I'm able to sign in on a non-Family Link device using the same account with no problem.
Sumit, do you happen to know if this is even on Microsoft's radar right now? Are they aware of people seeing this issue on Family Link Android devices? I've opened tickets and reached out to the Android developer email address but haven't gotten anywhere. Thanks.