Are savings or rental income enough?
Not for the M retirement visa. The regulation requires a certified lifetime pension of at least three Colombian monthly minimum wages. Periodic rental income may need a separate visa category assessment.
Which documents are often missed?
In addition to the pension certificate, the rule requires police clearance from the country where you stayed during the past three years, a medical certificate and health coverage in Colombia, with the applicable document formalities.
Can a retirement visa holder work in Colombia?
No. Article 77 expressly states that this visa does not authorize work in Colombia.