Customer paid products for free and product price shows free.

[Yancy]

I have a customer who ordered 6 items and the product price shows Free. The customer paid nothing for it. I received the order and it shows in Orders section.

I've checked the product also the website, the price is correct not $0.

Any causes for it? 

How can I prevent it from happening again? 

Appreciate for any help.

[ThePrimeWeb]

Hey @Yancy,

Can you share the link to your store? Just to test.  I promise I won't order anything for free 😊