You can create an account on https://test.instamojo.com
For payments use the following card details:
Number: 4242 4242 4242 4242
Date: Any valid future date
CVV: 111
Name: abc
3D-secure password: 1221
For API you can access your new developers credentials(API key, Auth Token 
and Salt) from here: https://test.instamojo.com/developers/