It keep saying "You must select an account for htis transaction." even though it has been selected under expense-cost of goods.

Hello @jackiecansell,

I was able to create a vendor transaction using the Cost of Good Sold account as the category detail. Let's consider logging into your QuickBooks Online account using a private or an incognito of your browser.

By doing so, we can identify why the error in red, saying you need to select an account, keep showing up. Let me guide you on how to open the said browser using a key shortcut on your keyboard.

• Google Chrome: Ctrl + Shift + N
• Mozilla Firefox: Ctrl + Shift + P
• Safari: Command + Option + P

If it works, have the cache of your browser cleared so your browsing experience can start fresh. If not, let's continue our troubleshooting steps by using other supported browser apps.

Additionally, I've got this helpful article for the steps of one of the methods in creating a vendor transaction: Enter and pay bills.

You can always leave a comment below if you have any other questions. Stay safe!