Hi there Ana!
My name is John and I'm a Guru here at Shopify!
Thanks for posting here about the 2Checkout error code you have been encountering.
I managed to find this 2Checkout support article which outlines some of the cases that can cause this error to present.
If you need any further assistance with resolving this I'd advise you to reach out to 2Checkout support so they can work with you on what might be causing this to trigger on your account.
Of course, if there is anything else I can help with please just let me know!
John D | Shopify