You have a few options of inviting past customers and/or visitors to your website to take part in your referral program:
Through newsletters using the Advocate Join Page link
Each ReferralCandy account comes with a Advocate Join Page link that you can use to get anyone to take part in your referral campaign. To invite people who are subscribed to your mailing list, include a link to your Portal Access Page in your newsletter to invite them to take part in your referral campaign.
Include a link on your home page
To let visitors to your website know about your referral program, you can include a link on your home page to the Advocate Join Page . Visitors can easily click through to the Portal Access Page to take part in your referral program. Or, make use of the embeddable sharing panel widget to embed a signup widget on your website for your referral program. Hop over to this blog post to see how others have done so.
You can send your Referral Email to anyone who's interested through the Invite Advocates feature. Learn more about this feature here.