Hello,
I am developing a mobile application with chatbot feature. What I want to learn is that I have one api key. Do I need to create a new key for each user using my application? How many requests can a key be used for simultaneously. Is there any limitation?
There is no limitation (or even tracking) per key, only per organization, in the current API.
However, you should not ship the key as part of your mobile application or configuration. You need to stand up your own web services server, that contains the key. This server should receive requests from your mobile app, and then forward appropriate requests to OpenAI.
Keeping track of which user uses how much of your server services, is up to you, and part of your server implementation.