Test selecting checkboxes using webdriverio and javascript

I am trying to test selecting checkboxes using webdriverio along with mocha, and chai.

Below is what I tried in a javascript module pattern

select_checkbox: function(browser, key, value){
  return browser.isSelected(key, value, 'tab')
},

I am calling this method inside a promise.each loop and submitting the form

...
     return reagents_utils.select_checkbox(browser, "#id_category_0", "Instrument");
}).then(function(){
    browser.saveScreenshot('./snapshot.png');
}).then(function(){
  return reagents_utils.submit_form(browser);
});

Here is a snapshot of tests showing that the checkbox is not selected and hence the submission fails!

How can test selecting the checkbox next to Instrument using webdriverio and javascript? I made sure that I am referencing the correct selector (id).