Welcome to Master Splat's atelier! Here you paint your own TeamSpeak channel image — 11 styles, all adjustable live. Pick the size for 3 or 7 channels, save it to the gallery and bring it to your server later. Nothing changes on the real TS until the admin approves it.
It usually works. The website bot is allowed to set channel banners on your servers — even on password channels.
If it fails for one specific channel during approval, it's almost always the modify power: the channel demands a higher „needed modify power" (i_channel_needed_modify_power) than the bot has (100).
How to fix it in TeamSpeak (as admin): right-click the channel → Edit permissions → set i_channel_needed_modify_power to ≤ 100 — or give the Ranking bot a higher i_channel_modify_power. Then approve again in the panel.