Сrucial steps:

1. You have to be an Administrator inside your Freshdesk.
2. Your Instagram account needs to be a Business type. Make sure it is NOT a Creator or Personal account.

• You can check that on Instagram.com by clicking Settings >> Account >> Switch account type
• If you see only personal and creator options, it means the Instagram account is correctly set as Business. If not, switch to a business account.

3.  Each Instagram account must be connected to a corresponding Facebook page. To find out how to connect IG account to a Facebook page, follow this article: How to link an Instagram business account and a Facebook page. The right connection should look the following way:

4.  You should be an Admin of your FB page (FB Page settings >> Page Roles):

5. Visit your Facebook Business Inbox for the connected account and check whether you receive DMs and comments there.

For example in Business Suite it looks the following way:

☝️If you do not receive DMs or comments in your FB Inbox, you should enable this feature, so that we could receive these messages on our end and pass them to Zendesk. Here're some articles that may help in this case:
https://www.facebook.com/help/772447486244207
https://www.facebook.com/help/1148909221857370

6. Check the Instagram account settings in Facebook Business assets and the permissions of the user who has created the integration. 

Make sure full control is given and all permissions are granted:

7. Visit Facebook Business Page settings and grant full permissions to the user who has created the integration:

Re-authenticate your Facebook page

1. Click on "Re-authenticate" inside the account settings:

2. A Facebook page will open. Click "Edit previous settings":

3. Select "Opt in to current Pages/Instagram Accounts only" and select all Facebok pages and all Instagram accounts you want to receive messages from, if you have more than one (meaning NOT just one currently re-authenticating):
     

4. Confirm the granted permissions on the next step by clicking Save:

5. You'll be redirected to OAPPS for Instagram Suite Account settings. Select the FB page you are connecting from the drop-down list:

6. Don't forget to save the changes! Click on the blue "Save" button first and only then Save in the lower right corner.