On Ardunio IDE 2.0.1, ESP8266 there is a compilation error (even for the basic examples)
/home/osboxes/Arduino/libraries/thinger.io/src/thinger/thinger.h:624:37: error: ‘class thinger::thinger_resource’ has no member named ‘then’
This is also present in 2.25.1 but 2.21.1 works fine.
I could not reproduce your issue, the example sketch compiled without issues, I would give a try to Platformio and VSCode or try to uninstall and reinstall arduino ide and the libraries.
Hope this helps.
Thanks! It looks like some issues with my IDE setup as it listed 2.25.2 as the latest, not 3.0.x I reinstalled and have it working fine on the latest Thinger library,