Llevo más de 50 actividades en cinta,¿Por qué no me dan medalla?

There are three main requirements for that badge:

1. All activities must be logged with a Garmin device.
2. The activity type must be set to Treadmill. You can edit that after the activity has synced if your watch doesn't have a treadmill activity type.
3. Only activities logged from 2020-04-28 will count.

An easy way to track the number of activities of a certain type is to create a goal: https://connect.garmin.com/modern/goals

Note that the goals will also count manually created activities which doesn't count for the badge.