I have a supplier that has also become a customer, how do I load this

You'll want to add this supplier as a customer, cabocraft.

Since QuickBooks Online doesn't allow two identical names, you can add a character or maybe a middle name for this customer.

Here's how:

1. Click Sales on the left pane.
2. Select Customers.
3. Click New customer.
4. Enter the name of the customer. Make sure it's not identical to their supplier name.
5. Enter needed information, then click Save.

That's it! You're now able to add this supplier as a customer.

If you got questions about the process, just leave a reply below.

Is there a way to merge them? Or else I will have to manage both accounts and reconcile manually.

Thank you for joining in the Community forum, @amar01.

Currently, you can only merge duplicates of the same type in QuickBooks Online. You can merge a customer with another customer, but there isn't a way to merge a customer to a supplier. 

However, you have the option to merge two accounts depending on its type. You can refer to this article for more details: How to merge accounts, customers, and suppliers.

Please know that the merging process is permanent and can't be undone at a later point. If you have follow-up questions regarding this process, do let me know. I'm here to help.