I managed to solve the issue. How?
The certificate activity was 'hidden for students'. Doing so, was because I do not want students to see this activity.
The certificate activity was 'hidden for students'. Doing so, was because I do not want students to see this activity.
But, when conditions were met, no certificate was issued. I did not have a clue. Also because I used this option many times, however, with some conditions as having a grade to pass.
Now I changed this property to 'Available, but not shown on the course page'.
Now, when conditions meet, the certificate is issued.