IMPORTANT: If you are an Admin of your Facebook Business Manager, unfortunately this does not mean you are automatically an Admin of the Business Page connected to your Instagram Business Profile.
Note: If you can see Instagram Insights on your iOS or Android Instagram app, unfortunately this does not mean that you have Admin access to the Business Page. In most cases, it means that someone else at your organization has previously converted your Instagram account to a Business Profile and simply given you the login details.
Here is how to check if you are an Admin of the Business Page you are trying to link to Iconosquare:
Step 1.) Please open pro.iconosquare.com in one tab, and open a new tab in your browser and sign into your Facebook personal profile (ex. www.facebook.com/john.smith) in this new tab. Then click this link: https://www.facebook.com/pages/?category=your_pages
Step 2.) Please select the Business Page you believe you have Admin access to. Next, click SETTINGS on the top right hand side, and then Page Roles on the left side. Scroll down; if your personal profile is not listed under ADMIN, unfortunately you are not an Admin of that Page. You'll need to contact one of the other Admins to grant you access. Once you have been granted Admin access, you should be able to try linking to Iconosquare again!
If your personal profile is listed next to ADMIN, then please proceed to Step 3...
Step 3: Please open the Instagram App on your iOS on Android phone. Next, click "Edit Profile" on your profile page, and under "Business Information" the associated Facebook Business Page should be listed next to 'Page'. Tap here to see the list of Pages you manage and to ensure that the correct Facebook Business Page appears with a check-mark next to it. If the checkmark is on a different Page, please select the correct Page to fix the problem. If the check-mark is on the correct Page, tap it again. If there are no Pages listed (or the correct Page is not listed), then unfortunately Facebook believes that you do not have Admin access to this Business Page.