Hi @arnaud.mergey,
Thanks for reaching out to the Auth0 Comunity!
To make your custom Action work, I recommend that you add a secret for the domain and the token respectively.
Our documentation on Adding a Secret for Action goes into further detail: https://auth0.com/docs/actions/write-your-first-action#add-a-secret
After you’ve included these secrets, your custom action will work.
Please let me know how this works for you.
Thank you.