Adding external materials to a Squarespace site

Hi, I'm thinking about creating but Squarespace website, but I have problems regarding the payment methods. Is it possible to use a homemade software design entirely for my requirements in terms of payment and to add such software to a Squarespace website for replacing what can't be done in term of payment with the usual Squarespace payment's setting. 

Thanks, have a great day!

Thanks a lot!

Do you know, by any chance, a platform which enable the use of external homemade software?

Does anybody know a website creating platform which enable the importation of homemade software for payments for example?