Why chasing goes wrong
Three mistakes account for most of it. Starting late, so your invoice misses the payment run and waits for the next one. Chasing the wrong person, usually the buyer rather than whoever processes payments. And escalating tone instead of substance, which turns a routine administrative matter into a relationship problem that is then harder to resolve than the payment itself.
The scripts below assume the opposite: start early, address the right person, stay neutral, and add facts rather than feeling as time passes. Adapt the wording to how you normally speak, since a message that sounds nothing like you reads as a template and is treated as one.