You can message a user using the ranking API with ease. This supports messaging any user on Roblox, and each successful invocation is counted against the 500 daily quota.
This only works on Hyra Cookie accounts. If you are using a Campfire Managed account please contact our team to request a transfer.
This route will send a user a Roblox Message.
The subject of the message
The contents of the message
The user you wish to message
"Message": "Successfully messaged user",