One of the feature of paypal is recurring payments. You can generate paypal subscription link url and send it to anyone who wants to purchase monthly or any periods recurring subscription.
Paypal subscription link generation is pretty simple and easy and can be done directly from your paypal account.
How to create paypal subscription link button
1. Login to your PayPal account
2. Goto: <topmenu> >Merchant Services
3. Look for “Sell Subscriptions” from the list on merchant services page
4. Enter necessary details and customize the subscription you want to provide to your users
5. Click create button
6. Now you have code in the box. You can either chose the paypal subscription button code in the box tab labelled “website” or click on “Email” to see the paypal subscription link code
Send this paypal subscription link to your users so that they can subscribe to your service on a recurring basis.