When this warning would be shown.

My client said that he didn’t get the email, even checking the spam email folder.

I’m using the default “custom registration form”, which is available to select the custom registration form by default of the system.

I have tried many times but still could not get the same screen as attached.

Are there any errors in my registration form ?
I have updated all the registration codes in the following post, (lastest comments)

Still strugling with your registration form ?
Or could you already solve it?

Yes, I am still struggling with the registration form.