Checkout tutorial lists invalid code.
General issue
Affected page: /guides/v2.4/howdoi/checkout/checkout_form.html
Description:
Implement the same custom checkout form into billing-step, with the below path does not work billing-step(children)->payment(children)->payments-list(children)->before-place-order(children)
Possible solutions:
Additional information:
When implement this on Billing step instead of shipping step we got the below error
and to reproduce the issue you should activate "Purchase Order" payment method then click on Place Order
most probably that's because there is another form for the Purchase Order Number

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Add a comment to assign the issue: @magento I am working on this
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@jfrontain can you take a look?