I would find it strange that you would receive a forbidden error. I would (with high load) expect a 503 error. You might want to file a support request on how to handle high loads and why a 403 is returned.
Regards,
Ronald
Thanks for the response. This may be due to how I am simulating the the problem as I do not currently have high loads but want to build for the off chance two requests are made at once.
I am using node-red to fire off 4 requests with the same message. I have concurrency allowed but I get the error message connected to concurrency of that microflow.