You have be the Admin of the Facebook page linked to your Instagram Business profile (under Page roles in your Facebook page Settings) to be able to post. Having Editor access is not sufficient for posting.
1. Log into your platform account and go to the social tool.
2. Please navigate to Services > My Services page.
3. Within the Services > My Services page select the option to Filter By Service Type.
4. Select the option for Instagram Business Profile.
5. Click on the edit button for the first Instagram Service.
6. Facebook will automatically pop up with the Admin account that has access to the Facebook Page and the Instagram Business Profile that are linked. Be sure to click on Edit Settings and NOT the name of the account in the connection box that is presented.
7. The next screen you see will have the following heading "Which Instagram Business accounts do you want to use?" This will show a screen of all available Instagram Business accounts associated with the Facebook Account you have accessed.
8. Ensure to select ALL of the Instagram Business Accounts that are presented.
9. Once all of the Instagram Business accounts have been selected click on Next.
10. The next screen you see will have the following header "What Pages do you want to use?". Ensure to select ALL of the Facebook Pages that are presented.
11. Once you have selected all of the Facebook Pages click on Next.
12. The next screen you see will have the following header "What will it be allowed allowed to do?" Ensure to select all of these options as without all of these options selected when posting from the platform to Instagram you may encounter issues.
If you find that any one of these options are turned off, please press the Back button and select all Instagram Business Accounts and Facebook Pages. Setting an option to no will cause your post to be rejected.
13. Once all of the options are enabled for all pages please click on Done.
14. You will then be presented with the final screen from Facebook advising you that "You've now linked the social dashboard to Facebook" from here click on the OK button.
15. Once the above steps are completed you will be returned to the Services > My Services > Edit Service screen.
Please ensure that the correct service is selected within the Instagram Business Profile: Select A Profile To Manage to drop down.
16. The final step in this process is to select the Update Account option.
17. You will then be returned to the Services > My Services screen. Please select the next Instagram Business Profile in the list and follow these steps to reconnect this.