As described on user manual, you need to define field name as idXxxxx, where Xxxx is an existing class of object.
For instance idBill will provide listbox containing list of bills.
If you need your own list, click on

to create your own list.

ok ... but After creating my custom list it does not appear as a list box
see attachements please

OK, Chef de Projet is a reference.
Did you call the field "idSomething" (start with "id")
If not, delete field and recreate.

NB : it seems your list of Chef de Projet is a list of Resource.
If so, it would be more easy to create new field ad "IdSomething__idResource"
"__idResource" (with double underscore will tell thet this field refers to list of resource

yes I always put the prefix "id" in the identifier of the field but...to obtain a list box
I Can not create a field with your precaunizations, an error message appears:
'idCdp__idResource' is not a valid field name.
Enter only alphabetic characters without spaces.
The first character must be a lowercase letter.
Close this message to reopen the field edit window
see attachment please

Sorry about "IdSomething__idResource"
It's available on developement version that is not released yet.
We'll work on it when 7.2.0 is deployed.

Can you post a screenshot of your definition of the custom field "Chef de projet" ?

Hello
here is the personalized list "chef de projet"
Thanks

I understand the issue.
The list should not be called "IdCdp" (Id not required). It should be just "Cdp". Then you add a field called idCdp.
For your list "IdCdp", the field must be called "idIdCdp" (it should work if you respect the case)