Once you have an Office 365 subscription, you have to renew within the same country.
You can’t buy an Office 365 package from one region/country and use it to top up an account from another region.
That might be tempting because of exchange rate and price differences but Microsoft won’t let you do it.
For example Office 365 Home is officially £79.99 a year in the UK. The US price is $99.99 or roughly £65. That’s 25% cheaper! It’s tempting to buy a US Office 365 Product Key and use it to renew your UK based Office 365 account – but that won’t work.
When you renew, your computer has to be (or appear to be) in the same country as the original Office 365 subscription. Microsoft has some geo-blocking in place but it can be bypassed.
For example, you’re from the USA and have an Office 365 subscription located in the US. However, you’re travelling in Europe when renewal is due. You can buy an Office 365 Product Key to download (eg. from Amazon US), no trouble so far.
When you try to add it to your Office 365 subscription you’ll get an error message saying that the code is incompatible with your region. That’s because Microsoft is detecting that the computer is outside the USA (using the IP address).
The workaround is to use a VPN or Proxy service so that it appears the computer is in the USA (in other words, it shows a US based IP address to Microsoft’s web site). Many services can do it; in fact, VPN is a useful tool for any regular traveler.
If that’s not possible, maybe ask someone back in the USA to renew for you. Give them your Microsoft account login, the new Product Key and instructions on how to renew.