Google Custom Search API returns 0 results for an indexed URL

I’m using the Google Custom Search JSON API to check whether a specific URL is indexed. However, even though I can find the page in Google manually, the API returns totalResults: 0

Here’s the URL I’m checking:
https://diario24horas.com/madrid/consigue-un-cabello-liso-y-saludable-con-un-alisado-permanente-organico-en-dim-salon/

And this is the request I’m sending:
GET https://www.googleapis.com/customsearch/v1?q=site:https://diario24horas.com/madrid/consigue-un-cabello-liso-y-saludable-con-un-alisado-permanente-organico-en-dim-salon/&key=API_KEY&cx=MY_cx

I get this response:
{
“searchInformation”: {
“totalResults”: “0”
}
}

a solution for my problem