Eureka! Success! I received my Pfizer vax (on top of 2x Moderna) at Parque del Colon (Parque de las Palomas). There was a center set up in the morning. There were few people and it was efficient. You never saw someone fill out an application so fast! I had my passport, my original vax documents and I am older than 65. No issues, no obstacles.
Side effects likely are influenced by individual responses. However, FYI, I was exhausted (fatigue) during the day and slept almost all day. That night I had mild malaise. Soreness at the injection site for several days. Personally, I prefer side effects as they indicate immune response.