When learning about Manager the best way is to create a test business and experiment.
That way the risk of any errors is low.
How did your experiment go. In case you are unsure these steps may help
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Create a test business
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Enable Receipts
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Create a custom field for payment. You want to enter some text in it, so start with a text field. Check show on printed document but not show as a column.
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Go to form defaults and copy the html code from the guide
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Create payment
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Look at the view screen of the payment