Is there any way to use variable name in API testing in Postman?

I'm testing the API using Postman (new to the API testing and has just started to test it), it was previously working as I use the variable name it stops working and displaying source code instead of the result.

Previously I'm using this API: https://reqres.in/api/users/2
After referring it to the variable it is now: {{url}}/api/users/2

Previously it is showing me result like this:

{"page": 2,"per_page": 3,"total": 12,"total_pages": 4,"data": [        {"id": 4,"first_name": "Eve","last_name": "Holt","avatar": "https://s3.amazonaws.com/uifaces/faces/twitter/marcoramires/128.jpg"        },        {"id": 5,"first_name": "Charles","last_name": "Morris","avatar": "https://s3.amazonaws.com/uifaces/faces/twitter/stephenmoon/128.jpg"        },        {"id": 6,"first_name": "Tracey","last_name": "Ramos","avatar": "https://s3.amazonaws.com/uifaces/faces/twitter/bigmancho/128.jpg"        }    ]}