Hi - I'm Aubrey
The examples you give are in languages I do not understand but if it is what I think it is, here is my proposal and understanding of your requirement
You are selling music files and when someone purchases one of them, you need a "One Time" code to be generated
This will allow downloading of the file only 1 time - after that it wont work
I have done this before and it should not take long
I will need access to the cPanel of the site as there will be a database tables to record the code, the file to be downloaded and to mark them as "Expired" once the download has been done
I will also provide an administration section for you to register new downloadable products and to reset specific codes if for some reason the download failed and the customer contacts you
You will also be able to see what was downloaded and when
This will not be attached to a payment portal - that is a different project altogether
Please PM me the site URL so that I can see various technical details which may affect the bid
Once I have seen your site I will be able to make a better estimation for the price, time and milestones
Look forward to hearing from you
All the best
Aubrey