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The ThingSpeak certificate was updated recently. If you are using secure communication for your devices, you may need to update the certificate or certificate fingerprint on your devices.

I've had a Thingspeak channel since 2017. It's updated by a RPi running Raspbian Lite (the Raspberry Pi version of Debian Linux). The "Lite" means there's not much GUI stuff in there, and the RPi is run "headless" using SSH. To update my channel I use the linux utility curl to send http GET commands. curl is run at intervals from a bash script which loops indefinitely.

This has worked fine for nearly 5 years until suddenly between 14:00 and 14:20 UTC on 13/4/22 (UK format) it stopped working, and I started getting HTTP error 400 responses. I haven't changed anything; I haven't updated the RPi OS for over a year, and the timestamp the bash script file is 2020.

Status is enabled on the channel, and a little trial and error showed that the problem was caused by including a status update string which contained a space character. So the workaround is simple, just amend the status string to not have a space character, and all is well again.

I can still send status updates with a string including a space character directly from a web browser, so what has happened to break curl after all this time?