Why does an 'unknown error' prevent product addition to cart?

[GabriellaM]

Hi!

I'm having an "Unknown error" with some of my products on the website.
I try to add them to the cart and the Unknown error window shows up below, not allowing the customers to add anything to their carts or complete purchases.

Any ideas?

Thanks in advance!

[Moira]

Hey @GabriellaM,

Welcome to the Community!

Do you have any third-party product-related apps installed by chance? If so, the developers should be able to solve it by re-indexing the website. Otherwise, for an immediate fix, you can remove the app completely. 

I have come across this issue a few times with various Pre-Order apps. Sometimes when they are not configured properly or clash with other apps within your store, we see errors much like the one you shared above. 

What is it that you are selling with Shopify?