Yeah, I think it's a signature key that may be downloaded.
I think that typically, what you purchase and obtain online is a digital decryption key or signature key. The program otherwise is complete in all its functional components but does not run unless a correct key is presented to it.
It is not the same as shipping a program without some required DLLs until the customer pays.
It also is not the same as replacing a trial or beta installation of a product with an entire new copy.
All of this is probably covered by prior art from early shareware - except for allowing the process to depend on Internet access.
Patents generally are required to be specific and achievable, I think, about what is done. I can't patent the idea of using the Starship Enterprise's matter transporter to obtain antimatter from inside the sun, because I don't specify how it works and I can't build it.
Rec[ntly, patents for business processes seem to have been allowed for inventions of the form, "We do exactly what people have been doing for years, but we do it on a computer." And then separately patented all over again with "computer" replaced by "mobile phone". That is ridiculous.