There might be multiple reason why Instagram is failing.

Case 1:

You have engaged massively with following/unfollowing, posting, liking/commenting, and so on. Causing Instagram to flag your account.
It is something that is not related to Publer, so you have to resolve the issue with the IG support team.

Case 2:

The Instagram user age is not verified:
To resolve the issue, you need to verify your age here.
Was this article helpful?
Thank you!