How do I get the non-deductible-amount to print in a receipt?

Question

The person bought a book and said 'round it up to x' as a donation. The person taking the order has gone

Contributions > New contribution > Credit card contribution

The 'non deductible amount' was filled out under 'Additional details'. The receipt was sent but it has no mention of the non-deductible amount.

I've gone into

Administer > Communications > Message template

and adjusted the 'online receipt' with

            <tr>
                <td {$labelStyle}>
                    {ts}Non-deductible Amount{/ts}
                </td>
                <td {$valueStyle}>
                    {$nonDeductibleAmount|crmMoney:$currency}
                </td>
            </tr>

This doesn't print out anything other than the heading. What is wrong? Variable is wrong? Wrong method or context?

This issue appears be similar to the following, which says that all bugs have been fixed relate to non deductible receipting.

Add 'Non-deductible amount' to Contribution Receipt template

Note that this question says that the bug has been fixed, although I am still experiencing the same issue on CiviCRM 5.14. It mentions varying symptoms. This question is differently specifically because it relates to 2019 and version 5.14.