entering balances brought forward for suppliers.

Hello, RobTW. 

Thank you for reaching out o the Community. It would be my pleasure to provide some insight into the debit and credit opening balance in QuickBooks Online.  

When entering customer or vendor opening balance, it'll impact other accounts. For customers, it'll affect Accounts Receivable and the income account for debit.

For Suppliers, it'll be the Accounts Payable and the Expense account for credit.  

For more insights about the opening balance, you visit this article: How to enter outstanding balances for customers and suppliers. 

If there's anything else I can help you with, please let me know. I'd be happy to get back to you and provide additional assistance.