Product key vs KMS: two different ways to license Office
Knowing the license channel tells you why one activation works and another keeps nagging.
A retail product key binds Office to your Microsoft account or device, one activation at a time. A MAK key activates a fixed number of machines directly against Microsoft servers. KMS, by contrast, is built for organizations: clients activate against a local server and renew periodically.
Why this matters for activation tools
KMS is designed to accept any properly formed local service that answers its protocol. That is what a KMS activator emulates, and why no internet validation from Microsoft is required. Retail editions, however, need to be converted to a volume channel first; a KMS service cannot activate a Home & Student installation.
Checking your current channel
The OSPP.VBS /dstatus output names the channel for each product. Look for VOLUME_KMSCLIENT or RETAIL in the license description rather than guessing from the edition name.