Venmo

 Venmo  is a payment application and social network owned by PayPal. In 2016-02, they stopped allowing new developers to use their API.

Documentation

 * https://help.venmo.com/hc/en-us/articles/210413477-Sending-Requesting-Money "If you’re on the web, click here to send a payment." emphasis added to indicate a hyperlink:
 * note: through experimentation, an   parameter also works
 * from previous documentation:   will preselect the user to pay as well.
 * all of these can be combined in a single link to select a note, amount, and username to pay.
 * See: payment for more.
 * See: payment for more.

Previously:
 * https://developer.venmo.com/docs/payment-links (previously described  links)
 * ^^^ unable to get this to work in archive.org - if you can link to an archive.org static copy (without JS) that works, please add it here!