Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
If you are trying to activate by telephone, call the appropriate number from the article at https://support.microsoft.com/en-us/office/-telephone-activation-is-no-longer-supported-for-your-product-error-when-activating-office-9b016cd2-0811-4cb3-b896-5a6a13177713.