Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Hi dadialla,
Thanks for the updates. I did a search in Office 365 URLs and IP address ranges and found this: activation.sls.microsoft.com
Normally we recommend turning off proxy when installing and activating since it will link to Office Online and many other URLs depending on different products and subscriptions, and if the above URL won't work, you could also do a search in the article I posted to check whether there are other URLs required for your environment.
At last, you could view some suggestions on this page: Using third-party network devices or solutions with Office 365.
Hope it could help: )
Br,
Oliver