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If you are using a Custom pay link you could add the URL to invoice emails that you send out. You could also use Method Portals to receive payments links to Method portals are already sent out when you send emails from transction screens in Method. You may also want to read this.
-Michael
Michael Melo
Product Manager
Method Integration Inc.
Website: http://www.method.me
LinkedIn: http://www.linkedin.com/in/MichaelMelo