The Agora RTM SDK does not have a limit on the number of concurrent online users. However, Agora has the following recommendations on the maximum number of messages per second for a single channel:

Concurrent online users in a single channel Number of messages per second
< 1,000 < 200
≥ 1,000 and < 10,000 < 100
≥ 10,000 < 30
If the number of messages per second exceeds the recommended values, latency can increase significantly and users may get disconnected. For scenarios requiring more messages per second, please contact support@agora.io.