Addtocart() not adding items to cart

We are offering additional services and we would like to have a checkbox with the additional services where clients can add them. The checkbox has one item (not an array). My code shows no errors but it does not add the product to the cart. Here is the code :

export function checkboxGroup1_change(event) {
 if($w('#checkboxGroup1').value==='Mailchimp Integration - $25'){
$w('#shoppingCartIcon2').addToCart("9b27")
}else{
wixStores.removeProductFromCart("9b27")
  }}

Any help will be appreciated!