The findOrCreate Salesforce Chat method begins the API call differently for Classic Live Agent Routing and Omni-Channel Routing. Please check the following for the difference:
The findOrCreate Salesforce Chat method begins the API call that finds existing records or creates new records when an agent or rep begins/accepts a chat with a customer for the Live Agent Routing.
For the chats that get routed by the Omni-Channel, the findOrCreate Chat code triggers even if the chat visitor cancels the chat before the agent accepts. Check the following article for reference.
