Error with preview and QR code

Good afternoon. I bought the premium version of the plugin. I use wordpress 5.0 and php 7.1. When trying to make a preview of the design it shows error 500. However, in this case it works, because I can make a normal test purchase with a credit card, and it generates the pdf by sending it to my mail.

But then, if I add a QR code in the design, I also get 500 error when trying to make the payment.

Please tell me what data you need to help me solve my problem. From already thank you very much.