Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Sandbox tenants are currently limited to eligible Visual Studio Subscriptions only, as detailed in this article: https://learn.microsoft.com/en-us/visualstudio/subscriptions/vs-m365#eligibility
You can instead sing up for a free trial: https://go.microsoft.com/fwlink/?linkid=2260943&clcid=0x409&culture=en-us&country=us