i want to build a digital download site ,i will send a link to my customer to check for the license/purchase key validation.purchase key will be provide my me when they download products.when customer input the license key by going to the link then the result will show them "Valid" or if not match then "invalid".I want to know the process,i am not finding the actual solution from google or youtube .can anyone suggest me that kind of plugin and system? Thanks in advance