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my mistake, sorry
I had configured an Authorization to the request, by default, with my environment so it provoked the error.
If I modifiy Autorization to "no authorization" it works.
To do so I configure all my body's data as parameters and I set the "Post QueryString" tickbox, I also configure a header Content-Type = application/x-www-form-urlencoded
It works fine.
sorry for disturbing
Alex