Does you script exit with a specific exit code?
255 is a general failure error code.
There are some examples that ship with Duplicati (not sure where they are in Linux) that can give you an example of generating a return code.
Try a simple script, such as “env >/tmp/env.txt” to verify that the script is being called, and then make sure to add an exit code.
Most scripts default to existing with exit code 0, but some commands will exit with 255.
Oh, and keep in mind that if duplicati is running as a service, it won’t have a profile, so you’ll have to set any PATH or similar requirements.
Share your script if you want some add’l thoughts.