Once everything on Stripe's end is set up, login to your account with us and find the Stripe integration under Admin > App Center:
You will be asked to enter your live Live Secret Key from Stripe.
To find this, open your Stripe account dashboard. Then click your username in the upper-right, and select Account Settings. You should get a pop-up window:
Click on API Keys, and copy the Live Secret Key into the software's Stripe Integration screen: