Many people have complained of issues with the Mexican government website (cvcovid.salud.gob.mx) where one’s vaccine certification document can be obtained.
Using WhatsApp is alternative that has less glitches, many users report. Simply send a message via WhatsApp to 561-713-0557, with the single word Hola. You will get a reply asking you to write the word CERTIFICADO. You will then be asked to enter your CURP number. You will then receive a link to your vaccine certificate, which you can download to your phone. Time taken: two minutes.