If there is an error, "Please add a Source URL" while scheduling, chances are that Tailwind wasn't able to find the Source URL, or the place where the Pin will lead to. There are a lot of Pins known as "Composite" Pins such as Promoted, Picked for You, etc, where Pinterest is "hiding" the Source URL on the page. It is very strange, we know, because you can clearly see that Pin has a URL! What we suggest to do when scheduling is scroll down on the page to load up some pins and then run your mouse quickly over several rows of pins- that makes it so the URL is now "unhidden". Then schedule, this results in the Pins all keeping their Source URLs.
Hover your mouse over a Pin before scheduling.
Schedule as normal with the Tailwind Scheduling Extension!
How to Schedule and keep Source URLs on Composite Pins video:
Helpful Tip: If this still doesn't work for you, make sure that your Tailwind Scheduling Extension (the schedule button) is up to date, and that you've cleared your cache and restarted the browser: Chrome, Firefox, or Safari.