How to bring the REMOTE ID of a commerce payment into the checkout completion page?
Unfortunately, because each order may have any number of payment transactions (meaning there is no strict 1:1 relationship), we cannot provide a simple token to make this available. You could create a custom Order token for the logic you know works on your site (e.g. [commerce-order:payment-id] that prints the remote ID of the first successful payment associated with the order). Otherwise you could customize the checkout completion page through a custom checkout pane, message text, etc.