Hi Tony LAUNAY,
Thanks for reaching out to Microsoft Q&A.
I hope you have followed all pre-reqs. Kindly go through step-by-step guidance once- https://learn.microsoft.com/en-us/azure/container-apps/key-vault-certificates-manage
Please do not forget to "Accept the answer” and “up-vote” wherever the information provided helps you, this can be beneficial to other community members