Working closely with UME on military dispositions of Catalan requetés, Sivatte was deeply involved in preparing detailed Carlist plans for rebellion both in Barcelona and in Catalonia. When the news of final deal with the military having been concluded arrived from Pamplona, on July 18 Sivatte and Caylá met to issue local insurgency orders, effective for the next day. From that moment onwards command over some 3,000 first-line volunteers and 15,000 auxiliaries passed to Catalan requeté leader Cunill. As the rebels failed, during two days of fighting the Catalan requetés were reduced to total disarray, some killed, some captured, some gone into hiding and some fleeing the region. Exact whereabouts of Sivatte are not clear; once the Republicans regained full control over Barcelona he went underground. Early August 1936 he managed to leave Catalonia for Marseille on a ship, disguised as a Polish citizen.