Matt,_log or perhaps in your Stripe logs indicating a connection?
Have you attempted to deactivate all plugins except WooCommerce, WC Vendors, WC Vendors Pro and the Stripe Commissions & Gateway plugin, and then tested to see if the vendor can connect properly? There could possibly be a plugin interfering with the Oauth from Stripe…
If you would please run the test above, and if that fails to isolate the issue, please provide me with an admin login & password in a PRIVATE reply so I can look at how you have things setup form the wordpress end. I cannot see your Stripe account… but one thing I can do is run a test to try and connect one of my own Stripe accounts as a vendor on your site.