If you have seen this error, it means that the account you are currently logged into with Snapppt is different from the account you are currently logged into Instagram with. What to do in this situation depends on what you are trying to achieve:
If you are trying to use Snapppt for a different Instagram account, then please see the following article: How to use Snapppt with a different Instagram account.
If on the other hand, you are trying to use re-authorise the current account you are already logged into Snapppt with, then you'll need to:
Head over to Instagram, and log out
Log back into Instagram with the account matching your Snapppt username
Head back to Snapppt and visit the 'Instagram Feed' tab which will re-authorise you
A final possible scenario is that you have changed your username at Instagram and want this reflected in your Snapppt username. This is a process that will happen automatically, usually in less than a day. If this does not happen for you, then please reach out to use.