hiding flat rate shipping when free shipping is available

I want flat rate shipping to be hidden when free shipping is available (only when ordering 8 items and more), I’ve added some code but it does not seem to be working. Is this because some coding due to the plugin? And how can I fix this?

I’m using the following code in my functions.php file:
// Hide standard shipping option when free shipping is available
add_filter( ‘woocommerce_available_shipping_methods’, ‘hide_standard_shipping_when_free_is_available’ , 10, 1 );

/**
* Hide Standard Shipping option when free shipping is available
*
* @param array $available_methods
*/
function hide_standard_shipping_when_free_is_available( $available_methods ) {

if( isset( $available_methods[‘free_shipping’] ) AND isset( $available_methods[‘flat_rate’] ) ) {

// remove standard shipping option
unset( $available_methods[‘flat_rate’] );
}

return $available_methods;
}