The LSIO docs says
DUPLICATI__WEBSERVICE_PASSWORD= #optional
but
DUPLICATI__WEBSERVICE_PASSWORD= #optional
is what you posted. Did you actually not give a password? You need to give one after = there.
DUPLICATI__WEBSERVICE_PASSWORD: "<ui password>" is what linked Duplicati manual shows.
I’m not enough of a Docker expert to say if : and = work the same. I’ll assume examples work
after you complete them. For Duplicati manual’s syntax, replace <ui password> with your own.