When using the Simplify SDKs, you may encounter an issue executing API requests with the error message 'Invalid or missing timestamp in JWS request message', 'Timestamp expired' or something similar.
This error is due to the fact that Simplify marks each API request with a timestamp and validates this against the time on our servers. If the difference between the timestamps is more than a 5 minutes you will get the error message you are seeing.
You or an administrator need to check that the time on your server(s) is correct and adjust it if not.
A good resource to use is http://time.is