Hello @AndrewO0 ,
First, you'll want to make sure you've setup a custom field to house that unique URL for the applicable contacts. Once you've uploaded your contact list with that information assigned to the proper field, then you can include it in an email. The most straightforward method of doing this would be using the Insert > Contact Details functionality.
Keep in mind, this would only include the URL as plain-text by default, it wouldn't auto-link from our side. While some email programs may auto-link the URL upon receiving, it would be wise to include a bit in the email mentioning that if the URL isn't clickable, your contacts can copy it into their address bar.
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