Currently we have a {receipt_link} email tag which outputs a hard-coded tag with the url automatically generated. The major limitation to this is if you are styling your email template you do not have the ability to control the color of that link at all.
Adding a {receipt_link_url} email tag will allow people to do something like this in their email template:
<a href="{receipt_link_url}" style="background: green; color: white; padding: 4px;">See your receipt online here</a>
@mathetos
Just started to work on this enhancement, and then I found the {receipt_link} email tag:
https://github.com/WordImpress/Give/blob/master/includes/emails/class-give-email-tags.php#L334
@ramiy it outputs a full anchor tag though, https://github.com/WordImpress/Give/blob/master/includes/emails/class-give-email-tags.php#L573
Matt is asking for just the raw URL

Has PR. Needs Testing. @mathetos
Tested, works, added a preview code in e7fa158c33bbc7059e3fa1ec93566687ac81e327
Closing
Most helpful comment
@ramiy it outputs a full anchor tag though, https://github.com/WordImpress/Give/blob/master/includes/emails/class-give-email-tags.php#L573
Matt is asking for just the raw URL