Not able to upgrade subscription plan with [renewform]

I am not able to upgrade my subscription plan if I register for FREE subscription plan. I have used [renewform] short code in my "Subscription" page. But it shows only my current subscription plan and other higher (paid) subscription plans, but doesn't show up the "Sign Up" buttons to upgrade my subscription plan.

When I debugged the "Subscription" page, I came to know that $gatewayissingle variable is getting value "admin".

What should I do? I have attached possible required screenshots below.