Error 'Couldn't authenticate you' in authorization process via API

I have my a Zendesk Chat App that has a search request.

Here is my code:

// Init the client 
const client = ZAFClient.init();

...

// Call the metadata first 
client.metadata().then(function (metadata) {

  ...

  const config = metadata.settings;

  ...

  const myZendeskSupportSettings = { 
    type: "GET", 
    url: `https://mysomesite.zendesk.com/api/v2/search.json?query=type:user example@mail.com`, 
    headers: { 
      "Authorization": `Basic ${config.my_zendeskd_suppport_token}` }, 
      dataType: "json" 
  };

  ...

  client.request(myZendeskSupportSettings).then((data) => {
    // does not reach this place, an error appears
  });

});

But when I try to make this request I get an error:

{"error":"Couldn't authenticate you"

How to avoid this error?