Hi Giles,
Welcome to Method! You'll need to set up an Accounts Receivable (AR) account in order to create an invoice. Here you can learn a little about what an AR account is. You may have not set one up in Quickbooks yet. You can also take a look at your Chart of Accounts in Method. You'll need to view your Quickbooks tab group (see my screenshot below to learn how to get there), and then go to Quickbooks Home>Chart of Accounts.
Jason
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Jason Masina
Community Support Specialist
Method Integration Inc.
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