A Source URL is the link that people visit when they click on your Pin. While a Source URL is not required to schedule and publish a Pin through Tailwind, including one is strongly recommended. Adding a relevant link drives traffic back to your website, helps your Pin reach a wider audience on Pinterest, and gives Pinners a reason to engage with your content.
Including a relevant source URL with all of your Pins is a best practice. If the content isn't directly promoting anything in particular (e.g., a blog post), you could set the source URL as your own website or similar, so long as it's related and something a user clicking the Pin wouldn't be surprised to be taken to.
Note: Pin Spacing rules are URL-based. If you schedule a Pin without a Source URL, Pin Spacing will not apply and the Pin will be scheduled to the next available time slot.
Helpful Tip: To see how to set the source URL on a Scheduled Pin, check out this article
URLs That Won't Work
There are a few source URLs that won't work though, such as any which point back to a Pinterest domain, or any links to spammy or inappropriate content as deemed by Pinterest.
If you are scheduling and pinning using the Tailwind browser extension, it will automatically detect and include the source URL for you!