Can't check IMEI on unlocked retail Apple iPhone 7+
I have a few leftover iPhones laying around and I'd like to give one to my brother in Michigan - he uses Boost Mobile. The phone I would like to give him is an iPhone 7+ (A1784) with iOS 13.2.2 and 256GB of storage. When I go to check this phone on the BYOD page is returns a weird message "We have good news and bad news...something went wrong on our end...try entering your device ID again..."
I've tried on 2 separate 7+ phones as well as an 8+ and always get the same message. I tried each IMEI number 3-4 times and I tried the MacID as well - same message over and over.
These are all phones that I purchased directly from the local Apple store and used for a short while on my AT&T account. They totally unlocked (were never locked) and none have SIM cards installed.
I'd like to get him setup with an iPhone but it appears that Boost can't use an iPhone 7+? I searched the forums and all I could find were where support folks had a direct message with people having this issue and no resolution was posted.