This issue is displayed when Instagram requires your to log into your Instagram account either through Instagram.com or the Instagram app to confirm your new login through Greatly Social. Instagram might display a popup asking if this new login was you, you will have to click "This was me" in order to connect your account in Greatly Social.
After this step is completed, please reconnect your Instagram account in your Greatly Social Account Manager page. Follow our guide on Reconnecting your accounts in Greatly Social.