Your module not working with the Sagepay payment extension.
After clicking the place order button, it renders the payment form, but the processing loader is not hiding.
We have written a custom module to fix the conflict between BSSCommerce One Step Checkout and Sagepay payment.
Please contact us and give your order number of One-step checkout extension at email@example.com then we'll send you that custom module.
If you need any further support, please feel free to contact us.
We'd like to help you.