How to activate MS Office

When I tried to activate the Office 2016 pro retail version. An error emerged saying that 'The Software Licensing Service reported that the product SKU is not found'.(error code 0xC004F069).Does anyone know how to solve this problem? Also, Is there anyway to activate the Office for free?

ERROR CODE: 0xC004F069 ERROR DESCRIPTION: The Software Licensing Service reported that the product SKU is not found.