AltServer could not sign in with your Apple ID. The network connection was lost.

Looks like this url https://gsa.apple.com/grandslam/GsService2 is not accessible.

NSURLErrorDomain -1005
Error Description
AltServer could not sign in with your Apple ID. The network connection was lost.
Failure
AltServer could not sign in with your Apple ID.
Title
AltStore could not be installed onto Dru's iPhone.
Underlying Error
Error Domain=kCFErrorDomainCFNetwork Code=-1005 "(null) Userinfo=LNSURLErrorNWPathKey=satisfied (Path is satisfied), interface: en0[802.11], ipv4, dns, uses wifi, _kCFStreamErrorCodeKey=57, _kCFStreamErrorDomainKey=1}
NSErrorFailingURLKey
https://gsa.apple.com/grandslam/GsService2
NSErrorFailingURLStringKey
https://gsa.apple.com/grandslam/GsService2
_NSURLErrorFailingURLSessionTaskErrorKey
LocalDataTask <59B81679-0239-4498-BB93-FF50916FC9D9>.<4>
_NSURLErrorRelatedURLSessionTaskErrorKey
"LocalDataTask <5981679-0239-4498-BB93-FF50916FC9D9>.<4>"
kCFStreamErrorCodeKey
57
KCFStreamErrorDomalnkey

Begin by reproducing the Apple ID sign-in attempt and checking access to https://gsa.apple.com/grandslam/GsService2. Then trace the Swift/iOS sign-in flow that calls this endpoint. Done means the -1005 failure is understood and has a verified resolution or a documented external-service limitation.