Cloudflare not sending invitation to add a new member

On my Manage Account > Members settings, I've tried adding new members to my account but the invitation emails isn't being sent to them. The status is Invite Pending, I double checked and the email address is correct, I've tried both on Firefox and Chrome without any extensions that might be blocking a request. I've tried "Resend invite" but it doesn't do anything, the email still doesn't arrive on the target account. I've checked both the inbox and the spam and the email isn't there.