Unable to send a new post with mailgun

My url is 4hab.fr. I run the lastest version of Ghost. I have configured Mailgun with the API key and DNS settings. My domain 4hab.fr has been verified.

But when I create a new post and try to send it to my own address (david.jamet@4hab.fr), I do not receive it.
When I try to send it to my suscribers, I get this message:
Capture d’écran 2021-07-22 à 10.53.11

Are you self hosting?

What is your mailgun plan type?

I am hosting Ghost V4 through a serious french hosting provider called OVH.
For mailgun, I have choosen their “FLEX PLAN / Pay as you grow”.
Thanks for your help.