The Plugin doesn’t work in my website. Help please

Hi, I am trying to use this plugin with a registration form created with formidable forms, but it doesn’t work and when I try to create a new account with the same email address used in another I get the message “This email is already present in our archives” and I can’t create the new account. On this forum I did find the link https://formidableforms.com/help-desk/allow-single-email-for-multiple-accounts/ to formidable form forum where they created a function for a user that use your plugin with formidable form and it seems to work reading the message. I did add their function to my function.php but I still get the same error message above. So I ask you way I can’t get your plugin work? I hope you can help me to solve this problem. Thank you in advance.