It seems that my saga with this issue is finally over.
The last update I received from their Level 3 support was that they were investigating a backend problem. Supposedly, there is a market identifier that is somehow blocking progress. I was advised to try accessing the service on mobile, but I encountered the same issues. While I was traveling, I also attempted to upgrade using a local SIM and a non-home IP, but that didn’t work either. I suspect that the problem lies on Microsoft's side since I tried using another device in a different country with a different browser and a new IP and ISP.
I figured out the resolution on my own. Here’s what I did:
- Navigated to "Manage Storage" - https://onedrive.live.com/?ocid=true&v=managestorage. Unfortunately, there were no options available to upgrade, as the buttons did not function.
- Navigated to "Plans and Upgrades" - https://onedrive.live.com/?ocid=true&v=upgrade&hideLeftNav=false. Here, I found four new buttons allowing me to upgrade. I’m not sure when they appeared, but it was likely sometime between now and a week ago, probably by the end of January.

- Clicked on the 10 TB button; it worked, and a new tab opened.
- Reached the checkout page, which detailed what I was purchasing, the price, and legal information. All the information was in the local language, regardless of my browser settings.

- Completed the payment using a regular card without any issues.
- Returned to OneDrive and saw that the 10 TB was applied, my Camera and Loyalty bonuses were still there. And a 1TB bonus for 365 family.
I have 11 TB in total now.

These sizes are a joke.

However, I noticed that my additional 1 TB subscription had disappeared. This had been part of my original subscription with 365 Family. Previously, I had 1 TB from that plan and an additional 1 TB as an extra - https://www.microsoft.com/en-us/microsoft-365/onedrive/additional-file-storage. This is how it looked before I purchased more storage today.

It seems that the extra 1 TB was canceled and replaced by my new package. When I revisited the "Plans and Upgrades" page - https://onedrive.live.com/?ocid=true&v=upgrade&hideLeftNav=false, the buttons to upgrade were still there. I attempted to purchase one extra TB, but received a warning indicating that I already had 10 TB and that adding another 1 TB would be considered a downgrade. It seems you cannot add more than one upgrade.


I also tried purchasing 10 TB a second time, and it went through, resulting in another charge. However, there was no increase in my total storage after this second purchase. When you buy an additional plan that matches your current package, it merely extends your existing subscription instead of giving you more storage. For instance, if your plan is 10 TB for one month and you buy another 10 TB, you won't receive an extra 10 TB; instead, your subscription will just be extended for one more month.
Overall, I consider this a success despite the unnecessarily complicated process. I hope they address the issue with the non-functional buttons on the "Manage Storage" page soon.