Hello @L1530 ,
Is your Instagram business page connected to your Facebook business manager , the one you log into with your personal Facebook account? Due to the way Facebook's (and Instagram's) API works, this page will need to be connected to that manager in order for us to connect to your applicable pages. Make sure to also confirm that the Instagram page is truly a business one, not a creator type. You also need to explicitly be an admin on the FB (and by extension Insta) pages you're trying to connect.
You may also wish to reach out to Facebook or Instagram's support if your business page continues not to show on your Facebook business manager, as there may be some other restriction on either one preventing it from being accessible on our side.
If this is in regards to connecting a Twitter or LinkedIn account, make sure you're also checking your page and account settings on that side, to see if there's any restrictions that'd be preventing 3rd party access. Their individual support pages can also help in this regard.
Change the Facebook Page associated with your Instagram Business Profile
Sync your social media accounts to create social posts through your Constant Contact account
Connecting LinkedIn accounts
Setting up LinkedIn business pages
Community & Social Media Support