The issue here is that you aren't giving any text/content for the message. So it's failing due to that. There is nothing to route/handle with blank messages. Neither text or content field is required on it's own (because you don't have to have both of them in each request), but you would have to have 1 or the other to get the message to inbound. I'm not sure if you've reviewed some of the docs on open messaging yet, but I would start there inboundTextMessages
Yes. I was about to respond to my own post that I figured it out. I found some sample messages (from that same link you provided) and got it to work.
I'm trying to integrate a 3rd party chat service with Genesys so the customer can be routed to an agent if necessary. I thought I could use Open Messaging and the empty inbound text was for the initial route request.
It sounds like you want something like this webmessaging/websocketapi#customer-join which is supported in webmessaging today, but not open, yet. Doesn't mean it won't be added to open eventually, but I can't give you any concrete timelines there. You could try to use webmessaging for your use case possibly.