Google Family Link Locked My Child’s Phone and Won’t Accept the Access Code

I’m having a serious issue with Google Family Link. Even though I entered the correct access code, the app keeps saying it’s invalid. Now my child’s phone is completely locked and unusable. It won’t unlock no matter what I do, even though the device is connected to the internet.

When I try to remove the supervision or unlink the account, it doesn’t work either. What’s worse, the app suddenly shows that my child’s account doesn’t exist and prompts me to send a new invitation instead. This makes absolutely no sense, and I have no idea what caused the issue.