This plugin is deprecated and should not be used for new installations.
PayPal API Subscriptions was built in 2008 using the PayPal NVP (Name-Value Pair) API v52.0, which PayPal has since discontinued in favour of their REST APIs. The plugin also directly handles raw credit card numbers on your server, which creates PCI compliance obligations that most WordPress sites cannot meet.
Recommended alternatives:
What happens in v1.2.0:
[ppsa] shortcodes display a retirement message instead of subscription buttons