Designer: Can’t add Shirt to Cart

Hi,

Thanks for your great plugin. While almost everything works smoothly on my site, unfortunately the spreadshirt designer is somewhat broken.

It is possible to design a shirt, but I can’t add it to the cart. As soon as I try that, I get an error message: https://photos.app.goo.gl/2qc5P6er88mRbg786

My site is https://www.polter-abend.at/polterabend-shirt-selbst-gestalten/

I don’t see anything suspicious in the JS Console.

Can you have a quick look? Did you experience before?

Thanks,
Lorenz