Secure connection for retrofit2.0

Question

I am getting error using retrofit2.0.

Mixed Content: The page at
'https://demo.myvirtualmerchant.com/VirtualMerchantDemo/process.do' was loaded over a secure connection, but contains a form which targets an insecure endpoint
'http://********/******/***/*'. This endpoint should be made available over a secure connection.", source: https://demo.myvirtualmerchant.com/VirtualMerchantDemo/process.do (0)

i am using dependencies

compile 'com.squareup.retrofit2:retrofit:2.0.2'    
compile 'com.squareup.retrofit2:converter-gson:2.0.2'    
compile 'com.squareup.okhttp3:logging-interceptor:3.4.1'

thanks in advance.