To get a successful response, make the requestTimeStamp match exactly the responseTimeStamp and you will get a successful 200 OK response. You can also use the time in the Response Header's "Date" but you should use the format month/day/year (e.g. 10/04/2019) and then you should use the exact time.
But my recommendation is for you to make the requestTimeStamp match exactly the responseTimeStamp, as that is easier for you to copy and paste. Refer to Request payload, Response payload, Response Header and screenshots below.
Try this sandbox test again and please share your results with us. I'm happy to help you with any further issues you may have.
"requestTimeStamp": "10/04/2019 5:49:59 PM",
"statusDescription": "Vendor is not configured for this transaction. Please verify",