That's caused by net terms orders.

The app is trying to redirect to a non existing page in your store, which results in a 404 error.

Head over to your offer > edit > scroll down > notice the net terms checkbox:

Notice the "Redirect to the following page after the order is created"

As such, the page will redirect to [].myshopify.com/pages/thank-you

If you don't have a thank you page - follow this guide to add it:

https://conversionbear.freshdesk.com/support/solutions/articles/48001199910-how-to-add-a-thank-you-page-for-net-terms-orders

Or, use a different address.

When redirecting to a valid page, you won't see any 404 page not found errors.