Need help with likes on an Instagram post via Facebook Ads Manager

Hi. I am trying to boost an Instagram post through the Facebook Business Manager (as there are more options to promote a post through Facebook Ads vs. just boosting a post on Instagram).

However, when I go through the whole process (selecting Engagement, getting charged by Impressions, etc.) and finally pick “Choose Existing Post” and select my post from Instagram, the likes go to a separate ad. They do NOT go to the existing post from Instagram.

My friends promote their post on Instagram through Facebook Business Manager and are able to get the likes right to the existing Instagram post. I walked through the process with them and am doing the same thing but don’t know why it’s not working for me.

Any ideas why Facebook Ads would create a separate post instead of sending likes to an existing post?

Thanks in advance!