Bid multipliers enable advertisers to reduce the amount of audience segmentation required because it allows them to maintain a nuanced bidding strategy within a single ad set with one targeted audience.
ads_management, ads_read, business_management permissions to update bid multipliers. Also make sure the ad accounts are associated with the system user that you are using to make the API call.fields=bid_adjustmentsads_management, ads_read, business_management permissions to check bid adjustments.