Fix PayPal notify url.
Fix the deprecated NOTIFYURL field name.
Update order payment amount before paid.
Add spec and some cs fixes.
Merge pull request #1246 from kayue/patch/update-order-payment

Update order payment amount before paid.
Merge pull request #1243 from kayue/patch-15

Fix PayPal notify url.
Add missing validation group.
Merge pull request #1250 from kayue/patch-16

Add missing validation group.