How do I get the review link for the after-delivery message?

From your Google Business Profile, not from Get Menu. On a computer: search your business on Google while signed in (or open business.google.com), press Read reviews, then Get more reviews, then Copy. On a phone in the Google Maps app: your profile picture → Your Business Profile → Get more reviews. The link looks like https://g.page/r/…/review. Paste it into Google review URL on Settings → Branding & logo; the review request under Automations only goes out once that field is filled.