Can't spectate or challenge certain friends

[Rhasimir-1573]

Are all of you running the same version? Mobile updates are usually delayed by a day or so.

See:

@Aelathera

Unable to challenge a friend on mobile?
If you are unable to duel a friend from your friends list, you will need to wait until both players are on the same patch.

You can check your build version on your mobile device in the Settings > Options menu. On desktop, you can check it on your Battle.net Launch next to the Play button.