Here is my schemas :

const candidatureCollection = {
  name: 'Candidature',
  fields: [
    { name: 'id', type: 'string' },
    { name: 'titre', type: 'string' },
    { name: 'benevole', type: 'string', reference: 'Benevole.id' },
    { name: 'annonce', type: 'string', reference: 'Annonce.id' },
  ],
};

const benevoleCollection = {
  name: 'Benevole',
  fields: [
    { name: 'id', type: 'string' },
    { name: 'structure', type: 'string', reference: 'Structure.id' },
  ],
};

const annonceCollection = {
  name: 'Annonce',
  fields: [
    { name: 'id', type: 'string' },
    { name: 'structure', type: 'string', reference: 'Structure.id' },
  ],
};

const structureCollection = {
  name: 'Structure',
  fields: [
    { name: 'id', type: 'string' },
    { name: 'nom', type: 'string' },
  ],
};

And here is my query on collection Candidature :

{
  "q": "*",
  "query_by": "titre",
  "prefix": true,
  "sort_by": "$Annonce($Structure(nom:asc))",
  "max_facet_values": 9999,
  "page": 1,
  "per_page": 10,
  "include_fields": "id"
}