Assuming you already Enabled chat service for your app from Design | Messaging | Chat page, if not, do it before starting the following test. Refer to this article for the detail.

Navigate to Design | Messaging | Chat Channels page, click [+New Channel] button and fill in the fields with essential values. Click the Save button to complete your creation.

You should find the channel you created on the list then.

Download the Unity chat example from here. Open the Chat-Example project through Unity Hub.

Test from the editor as shown below or build it into any platform that fits your test device.

Logging your app from the brainCloud setting tab:

Run the game, fill in the [User Name] and [Password] input fields with any words you prefer, and click the Authenticate button, you will see the success return like below.

Click the Enable RTT button from your Unity app, you should see the return as below with RTT connect success info.

Fill [Global channel code] field with the value "main" ( note: The full channel code looks like this “12020:gl:main” which is made in the button function. "12020" is your appId, "gl" represents a global channel, "main" is the global channel code.), click the Connect to Channel ID button. You will see the return info as below: (note: if you posted messages to this channel before, you will get a list of messages, otherwise, you won't see any messages here)

In order to post a message you will need to fill both Title and Message fields under the "Post Message" title. Once you post the message you will only get a debug log saying the post has been successful. You must connect to channel to see the messages associated with that channel.

Once a message is posted, click the Connect to Channel ID button to view all the messages in this channel in JSON format.

You can go-ahead to create a dynamic channel and test with it. Just make sure both users from Unity and portal are connected to the same channel.