Can't find reason for 400 error in SKY API call

I have been having an issue where the endpoint https://api.sky.blackbaud.com/gift/v1/giftbatches/{batch_id}/gifts returns an Error 400 RequestNotFulfilled with a message “The requested operation could not be fulfilled”, and that is all. I have a PHP script that hits this endpoint periodically throughout the day. Most of the time it works, but there are random windows of time, where the error 400 is returned. I’ve checked my requests’ bodies, and they are formatted identically when they work or when they don’t. The only thing different is the auth token, but it seems to be correct, since the error returned is a 400 error and not an auth error. Just wondering if anyone has had similar issues and what more I could do to troubleshoot the issue in this case? Thanks!