checkout error

I check allow customers to create an account during the checkout process, and let the customer can create an account only to type their email, and here is an error.

When my customer checkout without login , they can’t create an account in my checkout page,
when I deactivate this plugin, this error can be solved, how to fix it.

here is my product：

https://www.brain168.com/product/flystock/

here is my checkoutpage：

https://www.brain168.com/cart/

Best regard

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