We are creating payment gateways extension. But we are facing API connect issue. Please provide guide line. So we can easily implement.
Can you be a little more specific?
Which API is having issues?
Did you know there is are well known SagePay modules? Maybe you won't need to develop the whole integration.
Take a look at the Marketplace: https://marketplace.magento.com/catalogsearch/result/?q=sagepay