If i have overpaid a supplier and need to show that we are now in credit with them, how do I enter this?

You're already on the right track, @foulds-internode.

You'll have to create a bank deposit right after creating your vendor credit. This way, the credit will automatically be linked to the deposit. Then, you're able to show the amount when reconciling your account by the end of the month. Here's how:

1. Go to the + New button.
2. Select Bank deposit.
3. Go to the Add other funds to this deposit section, then enter the credit amount and all other necessary details.
4. Click Save and close or Save and new.

I've attached a screenshot below that shows the last two steps.

Kindly refer to the screenshot below for the outcome.

You can enter your credit depending on how you record your purchases in QBO. To learn more about this, you can check out this article: Enter a credit from a vendor.

By the end of the month, you can go ahead and reconcile your account. This is to keep track of your business real-life transactions and detect any possible errors accordingly. For the step-by-step guide, kindly refer to this article: Reconcile an account in QuickBooks Online. It also includes instructions about editing completed reconciliations.

Additionally, I'd recommend pulling up a vendor report. This is to effectively monitor your purchases and all your expense transactions. Just go to the What you owe and Expenses and vendors sections in the Reports menu.

Please let me know if you have other concerns. I'm just around to help. Take care always.