First of all, if you need to do payment with Meteor, I’d highly recommend using Stripe or Braintree. Their API is much simpler, better UX, everything … so why am I using PayPal?
Well Stripe is not in my country, and Braintree beta rejected our application because it’s a dating website!!!! *face palm*
Anyways, without much other choice, I went with the PayPal basic payment HTML form, submit to pay on their site, and return data with IPN (Instant Payment Notifications). It’s friggin stone-age technology but heck it still works.