Customer accounts must be enabled on your Shopify store admin so that customers can create accounts on your store and become members of your loyalty program.
On the Shopify admin homepage, click on Settings > Checkout.
In the Customer accounts section, click on Accounts are optional or Accounts are required according to your preference. Once done with your settings, click Save.
You can also go to the Customer accounts section by clicking Enable now in the BON Loyalty alert.