Assuming the Best
One of the easiest ways to keep your cool is to assume the best: There has been a mistake. It happens all the time, and mistakes are just that. Nobody is out to get you or to sucker you out of your paycheck. Something just got out of whack with the paperwork.
Even at a smaller magazine, say one that has seventy editorial pages in each issue, a managing editor will likely have to handle invoices from at least a dozen different writers each month. Think of all those papers moving from desk to desk throughout the payment-system chain, and you can easily see how an invoice might get misplaced.
The most common reason that magazines fail to pay writers is that invoices get misplaced or incorrectly coded for the magazine's business manager. When this happens to you (and it eventually will), try to keep in mind that the magazine probably already has a system in place to track your invoice down, correct whatever accounting codes are wrong, or figure out that you need to resend your invoice and start again.
A Good Editor Is Working for You
In this situation, you'll usually have either your regular editor or a conscientious managing editor working on your behalf to track down the lost or incorrect paperwork. Keep in mind that these editors don't relish this part of the job, either; it usually involves frustrated writers screaming at them over the telephone and bean counters making their lives miserable from a distant corporate office. If you can be the pleasant writer who is willing to help them solve the problem, you will likely earn their respect and any additional help that you might need should your problem escalate later.
The point is that you should assume the best — a mistake or misunderstanding — and do everything that you can to help the editor rectify it, even if it's not your fault.
There's a Fast-Track System
Sometimes, magazines have a fast-track system for getting invoices paid much quicker than usual. These systems are often designed to compensate for time lost to misplaced invoices and the like. If you can resend your invoice immediately to an editor who is trying to help you, then you just may get lucky and have your “lost” paycheck within a week's time.

