Hi mjooste,

Thanks for posting in the Community! Let's do some browser troubleshooting for you to be able to assign a GST when categorising a bank transaction. Sometimes too much cache accumulated in a browser might cause unexpected behavior with the product.

To start, access your account in a private window. This mode doesn't save any web searches and login details on your device. Here's the keyboard shortcut keys depending on the browser you're using:

• Google Chrome: press Ctrl + Shift + N 
• Firefox: press Ctrl + Shift + P
• Safari: press Control + Option + P

If you're able to select GST again in the drop-down list, go back to your regular browser and clear its cache. Or else, try using a different supported browser. It could be a temporary issue with QuickBooks and the current browser that you use.

Feel free to drop a comment below if you need further assistance. I'm here to help. Have a great day!