Is it possible to Use If statements in Web Services

I was trying to make a conditional web service PATCH. My code is as follows:

[{
    "if": [{
        "in": ["payroll", ""]
    }, {
        "op": "replace",
        "path": "/attributes/3352",
        "value": "13978"
    }, {
        "op": "replace",
        "path": "/attributes/3352",
        "value": "13975"
    }]
}]

It gives me an error that /"/" opperation is not supported. I don't know if the problem is with the If statement, the In statment, or if these opperations are not possible, or I have this coded wrong. Any help would be greately appreciated.