how i connect outside speakers to my imac

How did I connect an outside av receiver to my iMac 2019. I did it via a toslink adapter and an optical cable in my MacBook Pro 2013 and its works fine , but not in my iMac. No sound. I made the same configuration on both machines but works on MacBook Pro , but not on my iMac ? why? Did I forgot something or is a different way on the iMac ? Please help. I need to hear sound from my outside speaker in my iMac..