When you purchase the payment plugin, you will receive a zip file called os_eb_stripecheckout_unzip_first.zip. Unzip that file, you will get the file os_eb_stripecheckout.zip. Go to Events Booking -> Payment Plugins to install it as any other payment plugin. See https://eventbookingdoc.joomservices.com/basic-setup/payment-plugins#install-new-payment-plugin for installation instructions if needed.
Follow instructions https://stripe.com/docs/keys#api-keys , get your Stripe API Keys and enter it into the payment plugin parameters.
Follow instructions at https://stripe.com/docs/webhooks/setup#add-endpoint-dashboard, add the webhook URL below to your Stripe account:
https://domain.com/index.php?option=com_eventbooking&task=payment_confirm&payment_method=os_stripecheckout
(Of course, need to replace https://domain.com/ with your website url)
Select the event checkout.session.completed for that webhook URL.