Can not get the code to work

I installed “Code Snippits” plugin and added this code –
add_filter( ‘woocommerce_payment_complete_reduce_order_stock’, ‘__return_false’ );

but it does not help – the inventory is still being reduced with product purchase.

Not really sure how to use the plugin, but here is a screenshot of what I have –

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The page I need help with: [log in to see the link]