Hello Sir,
I have seen you videos. I have checked all the given links. This problem is with the API, Business Manager and your Site connectivity.
However, I have solved more critical problems than this.
I will solve the issue within two steps.
1. I will try to solve your current setup and will continue a day to check the issue arise again or not,
2. If step 1 doesn't work then I will setup everything again with proper process and will solve the issue.
BUT no worries, I will solve it and you will be happy to work with me.
My requirements:
admin access to page,
admin access to business manager,
admin access to website.
I will take 1-3 days to solve the issue.
Thanks You