Sending a message to an appointment's Teams Chat does not create the chat in Teams

Hi,

We are using Microsoft Graph API to send a message into a 1:1 Teams chat that's associated in the Outlook appointment.

await graphClient.Chats["{chat-id}"].Messages
	.Request()
	.AddAsync(chatMessage);

We have encountered a potential bug as shown below:

We have an Outlook appointment associated with a Teams Chat. (See attached screenshot related to the appointment), and the appointment has one organizer and one participant.

Assuming there is no such chat from the appointment in the Teams (no message history, no chat created/shown in Teams).

1. If the appointment organizer sending a request for a new message (chat-id from appointment.TeamsThreadId), the chat can be created/shown in the Teams and the message sent out successfully (see attached screenshot about the chat).
2. However, if the request was sent by the appointment participant, there is no error throwing from the response, but such chat wasn't created/shown in the Teams. (The message will be shown out when we manually opened the chat through Outlook appointment, which means the message was stored successfully)

Please give us any potential workaround for creating/showing chat when a participant (2) sending out a message into a chat that's associated into the Outlook appointment.

Thanks,

Percy