Open up Preferences and click on Shields. At the bottom of the page you will see a section for Saved Site Exceptions and then a subheading for Brave Payments. Just click the x next to the site you wish to contribute to again. Then, next time you visit the page, it should appear in your table again.
Here’s an example site:
Also, while doing this, you may see that the name does not display nicely in this section, I have logged an issue for this: