If you or one of your users are receiving a blank email from Google to gain access to Google Merchant Center. Then follow the steps below on how to accept your invitation.
Open your email address and view the original. In Gmail you can do this by clicking on the 3dot menu and then show original. Or alternatively right click anywhere on the page and view the source.
Search for notifications
Remove the equal signs from the URL as highlighted in the image below.
Copy the link, make sure to copy starting from https:// and stop the copy when you sell the word style
Below a demonstration.
Paste the copied URL in your browser, now you can accept the invite.
This solution was found by Jascom