Is your Instagram™ account a creator or business account? Instagram™ only let’s us connect these types of accounts. Here’s how to turn your normal account into a creator or business account.
Another problem could be that you didn’t choose your Instagram™ account in the Facebook™ pop-up that displays after clicking “Connect with Facebook™”. On the “Which Instagram™ Business accounts do you want to use with Neontools.io?” screen, you need to check the ones you want to use before clicking next.
A last issue might be that you didn’t give neontools the permissions it needs on the last screen of the Facebook™ pop-up. Make sure to give all the permissions required.
If nothing works, you can also try to disconnect Facebook™ and remove neontools permissions as describe here.
Here’s a tutorial on how to connect your social accounts.