When you're connecting Enji to your Facebook and Instagram accounts, it's best to give Enji access to all your pages—even if you're not going to actually connect them. Trust us, this has been the fix to a lot of people's struggles, so it's the best practice to make sure things go smoothly.
When you are in the process of trying to connect an account, when the first screen opens in the connection process, click "edit previous settings".
On the next screen click the "Opt in to all current and future Businesses" and then try to complete the process.