Check response code of request() call

[peterjaap]

Response Codes

The Measurement Protocol will return a 2xx status code if the HTTP request was received. The Measurement Protocol does not return an error code if the payload data was malformed, or if the data in the payload was incorrect or was not processed by Google Analytics.

If you do not get a 2xx status code, you should NOT retry the request. Instead, you should stop and correct any errors in your HTTP request.

[peterjaap]

Keep track of which requests did not return a 2xx status; maybe make a list in a grid?

[BasBlanken]

Log table might be overkill seeing normal users wont be able to fix errors,
maybe adding debug mode setting; if on, write error data to log file