Problem sending command

I successfully connected my Dragino LT-22222-L from TTS CE (TTN V3) to myDevices using the webHook. The data from the LT-22222-L are received and displayed.
When I try to transmit a value e.g. to switch on an output, I get the error-message “Problem sending command: unable to get local issuer certificate”.
What am I doing wrong or where can I find this certificate ?

can you share a screenshot of the error you are getting.

Thank you for your answer. Here the screenshot with the error-message:
I tried to actuate relay 1.