dataset search: query with white space

Hi,
I would like to emulate this browser query ([`fq=maintainer:Comune\%20di\%20Arezzo`](https://bit.ly/3M7J1r0)) 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