dataset search: query with white space

[aborruso]

Hi,
I would like to emulate this browser query (fq=maintainer:Comune\%20di\%20Arezzo) in the shell.

It works in the browser, but if I run

ckanapi -r https://dati.gov.it/opendata/ search datasets fq='(maintainer:"Comune\ di\ Arezzo")'

I have 504 error. What's wrong in my command?

Strangely the same query works via action:

ckanapi -r https://dati.gov.it/opendata/ action package_search fq='(maintainer:"Comune\ di\ Arezzo")'

Thank you