My client gets message like this while printing their invoice in email notification:
Your message: Response code 404 (Not Found
Did you test PDF Invoice by click Send test email in the Order confirmation setting page? Right?
Test order from order confirmation is just test data from Shopify. Absolutely, it doesn't exist in your store, so our app can't find it to print.
Furthermore, our app works with real data, you can create a test order to test it.
Here is the Shopify tutorial to create a new test order, you can read it.
Thank you for using AVADA PDF Invoice!