We've just released a new feature which allows you to invoice customers without dispatching stock. You will now able to invoice customers and take payment from them, then order the goods and dispatch the stock after you receive it.
To switch this feature on, go to Global Settings > Company > Sales & Purchases and under the Invoicing section, click the checkbox next to "Allow Invoicing without Dispatch."
Now, when you create a sale, you can click "Save and Invoice without Dispatching" at the bottom. Your stock levels remain unchanged.
Once you have received the stock and it is ready to dispatch to your customer, you can simply select the edit icon on the Sales order and click "Dispatch". Note: If you have batched items in the order, you must assign the item to a batch before you're able to dispatch.