The tokens you can use in a message template are a bit random, just what the developer added to the template. In this case, the contribution id can be found with {$contributionID}
. However, that is not the same as the invoice_number
. I could not find a token for the invoice number. But the templates are generated by smarty, and in smarty you can use the CiviCRM api. So the following line gets the invoice number:
{crmAPI var='invoiceReference'
entity='Contribution'
action='getvalue'
return="invoice_id"
id=$contributionID}
You can print it with {$invoiceReference}