I would like to check if the conversation was started by a message containing some specific keywords in order to decide what journey to give the contact.
For example, a Workflow with the Trigger "Conversation Started" can have a Branch Condition:
If "Last Incoming Message (Content)" contains the keyword "blue jeans"
, then don't give them the normal journey, instead give them send them a message specifically about blue jeans.
This is specially helpful, because some channels (like WhatsApp) allows you to add a pre-filled message to the URL, so people coming from that link will likely send that text and that will start the conversation.