I'm sorry, I have previously used that channel to display sensor data before for actuator control
I forgot to Do It against the Web2 URL
So I just did the Do It, hiding the evaluation in a debug procedure to not leave a trail of warnings and errors.
Notice how the URL has the https://api.thingspeak.com in front, but also so does your PostText!
Make up your mind.
P.S. Googling for Thingspeak Post Text got me to
Also, reread Noob's guide to Embedded Systems: Android App to connect to Thingspeak from my Web Services FAQ, where they set up Web2's URL.