Hi @AndresTorres94. Thanks for your question and welcome to the community forum.
Our REST API does not support Boolean operators (i.e., OR, AND). Instead, we score and sort the relevance of our results. So, the highest results in the API for your query https://0-api-crossref-org.brum.beds.ac.uk/works/?query.affiliation=Universidad+Pedagógica+y+Tecnológica+de+Colombia include matches for (ALL) the words Universidad, Pedagógica, y, Tecnológica, de, and Colombia. Comparatively, if you were to page through more of the results, you might find that you’d eventually only find matches that included (ONLY) the words Universidad and Pedagógica in the affiliation element.
On the first page of results, the first match returns a score of 69.39282, while the 20th result returns the score 64.30234 (the affiliation of that 20th result is “Universidad Pedagógica y Tecnológica de Colombia, Colombia” - so likely an affiliation that is a match for your query, if we’re only searching for exact matches).
If we expand your query and request 200 results - https://0-api-crossref-org.brum.beds.ac.uk/works/?query.affiliation=Universidad+Pedagógica+y+Tecnológica+de+Colombia&rows=200 - you’ll see that the 200th result receives a score of 40.76301, but the affiliations you’re requesting do not appear to be an exact match:
"family": "Rueda Ortiz",
"name": "Universidad Pedagógica Nacional"
"family": "Ríos García",
"name": "Unidad para la Atención y Reparación Integral a las Víctimas de Colombia"
This additional information should help you decide the threshold for acceptable matching.
Please let me know if you have any additional questions.