You might put the same message at the end of the setup(). put a delay(5000); just to make sure it’s all initialized and make sure the monitor is also set to 9600. If you see that message and not the interrupt message than the chain of neededs are not being met. Data stream on A2/D2 ? Interrupt actually being set to the same pin ? Data stream present and good logic high & low on the Xiao interrupt pin?