Resolve Instagram & Facebook Page Integration Issue

Fix Instagram "Boost Post" / Facebook Page Connection Error

Overview

I run a professional (Business/Creator) Instagram account, @mariamveiszadehdei, focused on diversity, equity and inclusion content, and I want to use the in-app "Boost" feature to run paid promotion on my posts. I need someone to diagnose and fully fix a connection error that's currently blocking this, end to end, so I can actually launch a boosted post successfully.

This is a fixed-scope technical fix, not an ongoing content or social media management role.

The problem

When I try to Boost a post from the Instagram app, it prompts me to "publish your Facebook Page Mariam Veiszadeh." That Page was previously deactivated (unpublished) on purpose and I do not want to republish it.

To work around this, I created and published a new, separate Facebook Page called "Mariam Veiszadeh DEI," intending to use that as the Page connected to my Instagram account instead. However, after creating and publishing the new Page, attempting to Boost still produces the same error, which suggests the new Page may not actually be correctly linked to my Instagram account yet, or there's a separate underlying issue.

What I've already tried

Attempted to republish the original deactivated Page directly, this fails with a generic "an error occurred" message.
Created a new Facebook Page, "Mariam Veiszadeh DEI," and published it successfully (had to clear a Meta SMS/identity verification checkpoint along the way, which is now resolved).
Attempted to change the connected Page via Instagram's profile settings, but the menu options I see on my device don't match standard guidance I've found online, so I haven't been able to confirm or change the linked Page myself.
Boost still fails with the same "publish your Facebook Page" prompt after the above.

What I need done
Diagnose why Instagram's Boost flow is still referencing the old, deactivated Facebook Page instead of the new one.
Correctly connect "Mariam Veiszadeh DEI" (or advise if a different setup is preferable) as the Page linked to my Instagram professional account.
Confirm my Meta/Instagram ad account, payment method, and any other prerequisites (Business Manager setup, ad permissions, account restrictions) are in working order.
Successfully launch a test Boost on one of my existing posts to confirm the whole flow works, from tapping Boost through to the ad going live.
Briefly document what was wrong and what was changed, in plain language, so I understand what happened and can avoid it next time.

Important constraints
Do not republish or reactivate my original "Mariam Veiszadeh" Facebook Page. It must stay deactivated.
Do not change my personal Facebook profile's privacy settings or visibility.
I'd prefer this handled via screen-share or a recorded walkthrough so I can follow along and learn the fix myself, rather than only being told "it's done."

Format & logistics
Fixed-price project preferred over hourly, given the narrow scope.
Timezone: Australia/Sydney (please note your availability relative to this).