PayPal Checkout is newer and better than PayPal Payments Standard. If you have subscriptions from another billing system, then you'll need to redirect those IPN requests and you should add mapping for those within the gateway in Blesta. See https://docs.blesta.com/display/user/PayPal+Payments+Standard#PayPalPaymentsStandard-CommonIssues for more on doing a redirect.
Note that PayPal Checkout IPN calls can interfere with PayPal Payments Standard, per the alert at https://docs.blesta.com/display/user/PayPal+Checkout It's generally a good idea not to use both.