This Meta-side error occurs because the removal of the deprecated Instagram Explore Home placement from Ads Manager has not yet been reflected in the Graph API.
The Meta team is aware and working on a fix. In the meantime, you can either
Manually remove the Instagram Explore Home placement in Ads Manager from the ad set settings that are returning this error.
Or
Turn on the Advantage+ placement option.
In order to make one of the changes mentioned above, please navigate to the campaign's ad set → Placements → Manual placements → uncheck Instagram Explore Home/select Advantage+ option→ save.
In case further help is needed, please reach out to us via chat bubble or at support@bir.ch.