To do this, you need to create a custom field under Settings > Custom fields on invoice level. As type you choose “number” and you give it a name, e.g. “Transaction number”.
Once you have created the custom field, go to Settings > Document layout and click on “Invoices”. You then get to see “Shortcode list” on the righthand side. Click on it and search for the shortcode of the custom field you just created since we need the number of it. As soon as you know this number, get in touch with us via email@example.com so that we can activate the preference “invoice_paid_add_customfield” for your account.
In the example below, the number we would need is 34505.
Once this is activated, you can add a transaction number when you set your invoice on paid.
Customer support service by UserEcho