For my setup, an arduino UNO with ESP, these sketches don't compile.
I tried that for a long time, without success, without getting any further.
Moreover, it seems nobody with arduino uno and wifi seems to use these examples nor the thingspeak library to build on (based on different googles). Instead they try to post with GET.
With the above only the posting itself just doeas not happen.
No help in the tutorial, nor in the examples, only a week of lost time.
Geert