I am fairly new to Cvent, but I have used the Voucher Code field before. The drawback is that once you enable the Voucher Code widget in your registration process, a code is required in order to register. So, if someone doesn't have a referral code, they won't be able to register. It sounds like an additional question might be the better way to go in your situation. You can create a question with an open text box answer field or a drop down with pre-determined answers and leave it as not required or update it to be a required question as your event needs. You can then run a detailed report with answers to your registration questions, export to Excel, and filter the data to pull the information that you need.
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Jess Olcott
Training Program Coordinator
ETC, Inc.
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