Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Hello, good day and thanks for your question. Sorry to know about this issue that you have encountered when you tried to redeem your Microsoft 365 Family.
For this, please check and try this on a different browser or also use inPrivate or Incognito browsing and see if it will push through from there without an error.
If it is still the same, you can reach out to the support team at https://support.microsoft.com/en-us/contactus/ and then click on Microsoft 365 and then click Get Home Support and then type in License issue and click the blue button that says Sign in to contact Support and login and provide them with the product key for them to check if the store where you bought this from has correctly registered the key after the sale on the Microsoft system and if Microsoft Support is unable to resolve the problem then you will need to contact the store to get a refund or a replacement key.