If you are using our Stripe Commissions & Gateway Plugin…
You set up your Stripe Connect in your Stripe account as admin, as we show in our set-up guide: https://www.wcvendors.com/kb/stripe-commissions-gateway-setup/
When using WC Vendors Pro, the vendors can then add their own Stripe account from the dashboard: pro dashboard > settings > payments by clicking on the “connect to Stripe” button. It sounds like this is where you are experiencing an issue…
Are you testing in a live environment or the testing environment?
If Live, DO you have a redirect URL set for the “Production” field in your Stripe settings?
when you look in your Stripe account for connected accounts, does it show that any of the vendor accounts did actually connect to your platform?