Calendar people don't receive my invitations

Hi the community,

I am trying to use iphone calendar on my iphone 12 with my icloud.

I have enable to synchronise calendar on all my devices in the icloud app.

I can receive invitations from my friends on my icloud calendar. But once i want to send invitation, i can see the event on my side pending an anwser but my friend don't receive the invitation.

My apple ID is a xxxxx@gmail.com for your information.

I tried to several people, my internet connection is good,... i dont understand.

Thanks!