Microsoft Word for Mac, version 16.66.1 and macOS Catalina 10.15.8

Hello, I need help with activating my existing Microsoft 365 Personal subscription on my Mac.

My situation:

• I have an active Microsoft 365 Personal subscription.
• The subscription was purchased through the Apple App Store.
• My Microsoft account is the correct account associated with the subscription: ******@mail.ru
• When I log into my Microsoft account online, it clearly shows: “Microsoft 365 Personal — Purchased from Apple.”
• The subscription is also active in my Apple App Store subscriptions.
• I am using Microsoft Word for Mac, version 16.66.1.
• My Mac is a MacBook Air 13-inch, Mid 2012, running macOS Catalina 10.15.8, which is the latest officially supported macOS version for this Mac.
• Word shows “Belongs to: ******@mail.ru,” so the correct Microsoft account is being used.
• I successfully completed the Microsoft account verification/security-code process.
• However, when Word tries to activate, I receive: “Unable to associate your purchase. Your purchase was successful, but we weren't able to associate it with your Microsoft account.”
• Word then also produces “Unknown Error” with error code 0x0.
• Word is currently in reduced functionality mode and says “Subscription Required to Edit and Save.”

I have already signed out and signed back into the correct Microsoft account, but the same error occurs.

I also cannot use the current Office/macOS update solution because my 2012 Mac cannot officially upgrade beyond macOS Catalina.

Could you please help me restore/associate my existing Apple App Store Microsoft 365 purchase with my Microsoft account, or manually resolve the App Store receipt/license association?

I do NOT want to purchase another subscription. I only want to activate the subscription I already have.

Thank you.