It appears that your are charging EUR 10 for removal of "Powered by Deftform" and if it's purchased as an Extended add-on together with sending emails from custom domain, then it's EUR 19 as one-time payment. Since this LTD already includes a custom domain feature, why wouldn't removal of "Powered by" and ability to send emails from custom domain be part of it? It would make for a far more valuable tool :-)