With the release of World of Warcraft Classic 1.13.3 15, we’re making a change to disallow calling C_ChatInfo.SendAddonMessage with the CHANNEL ChatType. This will prevent addons from communicating over custom, player-created chat channels.
Addons will still be able to communicate using PARTY, RAID, GUILD, and WHISPER in the same ways that they can now. Additionally, we are going to test a change to permit C_ChatInfo.SendAddonMessage to be called with SAY and YELL, allowing your addons to communicate with players in your immediate vicinity.
We support using addons to customize your gameplay experience. However, we also want to ensure that we preserve the social dynamics that make Classic what it is. Ultimately, we decided that the ability for addons to send invisible messages to large, arbitrary groups of players all across Azeroth was something that risked undermining those social dynamics.