httpss instead of https on “Go to checkout” link

When I am on a product page and I add a product and the “Go to checkout” notification pops up it is an httpss link (an extra s) so it doesn’t work. I’ve been using this plugin for a longggg time, not sure I ever remember this being an issue. How can I fix it?

https://www.patioslingsite.com/products-page/chair-replacement-slings/replacement-chair-sling-1pc/