If you are receiving an error "504 Bad Gateway" when you attempt to link your Battle.Net account, please try the following steps:
- Log in to your Battle.Net account: https://battle.net
- Go to: Account management > Security & Privacy > Authorized Applications
- Remove "Raider.IO" from the list
- Log in on Raider.IO and re-sync your Battle.Net account. Make sure to grant access to your WoW account.