Does Weebly offer a true shopping cart? If not, the easiest thing to do might be to sign up for a third-party shopping cart that works with PayPal and which can handle digital goods. The customer will place the order through the shopping cart which will process the payment and redirect them automatically to the appropriate download page.
In addition, PayPal itself says they offer an automated, hand's-free way of selling digital goods: https://www.thepaypalblog.com/2011/0...digital-goods/
If this is beyond you from a technical standpoint (and don't feel down if it is -- lots of folks struggle with this), you might be well served to spend a few dollars to hire someone to set up and configure things for you, and train you on how to operate it all.
In the end, the money you spend on that will be far less than the value of the time you save not having to send all those manual emails and the increased customer satisfaction from instant downloads when they make a purchase.