I created an article in a shop with two custom fields, one field to upload an image, other field to submit a URL.

My question now is, in the acp under transactions I can only view the buyers information but not the values of the custom fields. Where can I find the field values? Thanks.

To answer it by myself and if someone faces the same situation:

Go to Payments --> invoices --> click on the title of the item  ---> in next window click on item and there you can see the custom fields the customer has filled in.

But, this only works if you have renewal enabled, without you can't click onto the item. It's a bug.