paypal-callback.js

paypal.Button.render({

   payment: function(resolve) {
       getPayPalToken(function(token) {
           resolve(token);
       });
   },
   
   onAuthorize: function(data) {
       getPayPalTokenDetails(data.paymentToken, data.function(details) {
           console.log(details)
       });
   }
}, '#container');

function getPayPalToken(callback) {
    jquery.ajax({
       url: '...',
       success: function(data) {
           callback(data.paypalToken);
       }
    })
}

function getPayPalTokenDetails(token, callback) {
    jquery.ajax({
       url: '...?token=' + token,
       success: function(data) {
           callback(data);
       }
    })
}