Error on "Update reference for"

In your phrase you mix update reference for "Activities" and "change reference on type or project change : No" that don't has same effect.

Can you explain your use case ?

Thank for the explanation. It's clear.

In facg, reference numbering works as expected.
Just a short explanation.
In peojeqtor, each item has an id, which is shared amonst all items of same class, for all projects.
This means that if you create a first ticket for project 1, it gets id 1.
Then if you create a ticket for project 2, it gets id 2.
And if you create another ticket on project 1, it gets id 3. So tickets on project 1 are 1 and 3 : there is a hole in the numbering.
Idea of reference is to provide a number that will be unique for a given project and/or type.

You defined a prifi {PROJ}-{TYPE}-
So numbering will be unique for Project code and Code of type.
If you want unique sequence for all items of same project, you need to define reference as {PROJ}- only, or define same code for all types of activities.