The {{invoice_total}} tag that is included in the default SMS template sent when a ticket is marked completed (and has an invoice attached to it) sends a complete total for the invoice that disregards any pre-payments or deposits made, I'd suggest you change this to include the BALANCE DUE total on the invoice which would cover every business who uses your software's needs, including the ones (like us) who may get pre-payments/deposits for certain parts or flat rate services.

This has caused several panicked or angry customers to call for an explanation from us over time :)

I attempted to find a template tag that I could change the SMS template to include this balance due but couldn't find one, so if there is one I can use maybe this suggestion isn't a needed change and this post will at least help someone else who's situation matches ours.