New problem with my Payment button (API code?)

I don’t know if this is a Snipcart problem or a Sparkle problem.

I have several buttons that add items to the cart. They all work fine.
I just tried to add some more buttons, but they give me an error when I try to checkout with PayPal.

The error says " Price of products in the cart may have changed. Try removing and adding them to your cart. Please contact the store owner for details."

I can reproduce this error with the new buttons, but all of the old buttons still work.
I had created the new buttons by copying & pasting the buttons already in use. When they failed, I tried creating new buttons but get the same error. Normally, I copy/paste the working button all of the time, but all of the times I’ve used it in the past are for items that have the same price. But all of these new buttons that are failing are adding items of a different price.

All of the items on my site use the same API code. Or should I have created a unique secret API code for each item that has a different price? The documentation is unclear to me, and I’m reluctant to try to add a new API key until I know that I’m not going to break these rest of my site.

The single API key should work. Do you have a published page where the problem happens so I can take a look?

Here is the page with the payment buttons.
Chess Curriculum

I can add items and change the quantity. But when we try to continue to PayPal to pay, that’s when we receive the error.

And as a comparison, here’s a page with working products.

Something is odd there, I think it might be best if you send us the project file ( to and we’ll take a look.

I’ve just sent the file to you.
It’s only 12MB, so I was able to include it as an attachment.