To use the tellraw feature, follow these steps:

• Create a file called `chatmotd.json` in the ChatMOTD plugin directory.
• Paste the exact JSON for your tell raw command, eg, the bit after the selector in the vanilla tellraw command.
• If the `chatmotd.json` file is present, it will override the motd in `chatmotd.txt`. You also can't use `/setchatmotd` when the plugin is using `chatmotd.json` as Minecraft chat doesn't support enough characters to paste all the JSON in correctly. You must just edit the file directly.

You can use a tellraw generator like this one.