In order for Megalytic to connect your Facebook account, you must have an email address associated with your account. You may refer to this link for instructions on how to add an email address to your Facebook account.
When this happens, it means that Facebook is not providing Megalytic with the email associated with the account you are logged in to Facebook (FB) with. Usually, that happens when the FB account does not have an email (i.e., it has been set up with only a mobile phone number). But it can also happen when the account’s FB email is not verified. When a FB account gets created with an email, or an email gets added to the account, FB sends a verification link to the email address. But, sometimes the recipient ignores or misses this verification email and then the email address on the account remains unverified.
To solve this, you need to force FB to send a new verification link, so that you can verify the email on the account. You can do this by changing the email address on the account, and then changing it back. FB provides the steps here.
Alternatively, if you have access to a different FB account that has permissions for the Page you want to connect, then you can log out of your current FB account and log in to the other one that has access. Here is a video to show how you can log out/in of different FB account for authorizing Megalytic connections: Connect to Facebook Page from Different Facebook Accounts