Why back-end methods fail on received webhook but succeed when run manually/supervised

Thank you for prompt reply — I appreciate that!
To answer your questions:

  1. An external app is POSTing data to our WiX endpoint, we’re handling it using wix-https functions
  2. The code on the WiX side results in the “undefined” error
  3. The same data is handled correctly if we run the same code outside the http-function

I will have to clean up the code before I can publish it