Each person could cast a single vote, which could be done via the web votacionessanfermin.pamplona.es/eu/ until the suspension occurred. A jury selected 10 of those submitted to the competition, and from there the popular vote had the floor.
The voting website is run by a public company of the Administration of Navarra, Animsa (and numerous computer services and municipal websites in Nafarroa Garaia), which announced that a particular cartel was receiving in a few hours a set of extraordinary votes. You did not say what the cartel is, but the decision was drastic, you interrupted the vote.
The ten finalist posters can be seen here.