I'm ready to add subscriptions to my consumer saas project. It is a Gmail addon accessed through a web app and chrome extension.<p>I have a fremium model, with multiple levels of upgrades.<p>Can anyone recommend a solid payment platform that a one person dev can implement with minimal fuss?<p>I need subscription support (monthly, annual), security, and straightforward apis. Also, I don't want to store any card numbers in my app.<p>Is anyone using chargify to handle the account management part? I like the feature set but it gets expensive as you scale. I could spend time upfront to code those features myself.<p>My app is written in Python running on Google app engine.<p>Thank you.