Yes, you can input purchases under the Category column when recording your expenses in QuickBooks Online (QBO), @userhuini. 

You have the authority in choosing the right expense account (i.e. Purchases) when you create an Expense transaction. In QBO, the Category Details refers to a selection of an account from the company's chart of accounts to categorise your expense type.

The first solution provided may have based on a different scenario. That's why it lets you categorize your expenses to either the Accounts Payable or Trade and other Payables accounts. After drilling down the situation, you can simply enter purchases in the Category column or any expense account that match or categorise your transaction details.

Please see the screenshot below.

To learn more about the sections in an Expense transaction, kindly refer to this article: What is the difference between Account Details and Item Details sections. it clearly explains the Item and Category sections in your expense transactions.

You can record your expenses by creating a bill, cheque, or expense. To learn more about their differences, here's an article that describes when you can use any of the mentioned transactions: What is the difference between bills, cheques, and expenses?.

Select the Reply button below if you have a follow-up inquiry or other concerns about recording your expenses in QBO. I'm just around to help. Take care.