Savedata transfer ("nn::migration::savedata::IServer"/"nn::migration::savedata::IClient") requires that accounts are linked to the same network-account. acc:su [[NS_services#IManagerForSystemService|IManagerForSystemService]] GetAccountId is used here. The server stores this Id into state, and also stores it in the [[LDN_services|ldn]] AdvertiseData. The client also verifies the Id in AdvertiseData against the Id from GetAccountId for the account(s) being used, during ScanServersAsync.