What is the easiest way to include a payment link on an email for an invoices notification? We use cybersource as are gateway, if that is helpful.

Cybersource has a hosted payment solution but it is not integrated with NetSuite. You will need to get a 3rd party app for doing this. I know that SCS Cloud has a good one and they are NetSuite payments experts. https://netsuite-payments.scscloud.com