for Standard editions. Activation methods involve direct key entry, Microsoft Account association, KMS command-line, or telephone activation, though using unauthorized keys may breach licensing terms. For a guaranteed, legal installation, it is recommended to use official Microsoft channels. For details on troubleshooting activation, visit Microsoft Q&A Microsoft Learn How can i get Office 2016 product key - Microsoft Learn
"Key Already in Use": This happens if the key is tied to another Microsoft account or device. Ensure you aren't exceeding the installation limit. Microsoft Office 2016 Product Key -Activation 100- Working-
The key is formatted in five groups of five characters, looking like this: XXXXX-XXXXX-XXXXX-XXXXX-XXXXX for Standard editions