Dear William Noonan,
Welcome to the Microsoft Community.
I understand that after purchasing Word you are prompted to subscribe to Microsoft 365 when you open the application, I understand when you are experiencing problems and will do my best to help you.
I would like to confirm with you that you are viewing the product information in the Services & Subscriptions screen of your Microsoft account? You can confirm this by clicking the link below and logging into your Microsoft account: Microsoft account | Services and Subscriptions
The above error may occur if you have purchased Word but have installed Microsoft 365, so I would like to do some troubleshooting with you first:
You can first cleanly uninstall the current Word program and clear the licence, then reinstall to try:
1. Clean uninstallation:
Uninstallation through the uninstallation support tool: You can install the uninstallation from the link below, it will take a few minutes to download and install the programme. After installation, the ‘Uninstall Microsoft Product’ window will open.
https://outlookdiagnostics.azureedge.net/sarasetup/SetupProd_OffScrub.exe
2. Remove the licence: How to remove Office license files on a Mac - Microsoft Support
remove tool:
https://officecdn-microsoft-com.akamaized.net/pr/C1297A47-86C4-4C1F-97FA-950631F94777/MacAutoupdate/Microsoft_Office_License_Removal_2.7.pkg

3. Reinstall:
If you can see the Word product in the Services & Subscriptions screen of your Microsoft account, you can install it directly under your account: Microsoft account | Services and Subscriptions
Sincerely hope that you can understand, because the initial information may not allow us to clearly understand the depth of the problem, if you need further support, you are welcome to contact us at any time.
Thank you for your understanding and wish you all the best.
Best regards
Isabella-MSFT | Microsoft Community Support Specialist