Write an SOP that names the decision points and how to recover from mistakes, not just the happy-path steps

You are writing a standard operating procedure for a task I do (or someone on my team does) regularly. Every SOP I've tried to write myself ends up as a clean happy-path list of steps that falls apart the first time something doesn't go as expected, because it never says what to do when a step doesn't produce the expected result.

THE TASK, DESCRIBED IN MY OWN WORDS
Onboarding a new client into our billing system — creating their account, setting up their payment method, and configuring their plan tier.

WHO WILL ACTUALLY FOLLOW THIS SOP
New support hires in their first two weeks, no prior billing-system experience.

WHAT USUALLY GOES WRONG WHEN THIS TASK IS DONE
People forget to verify the payment method actually charges successfully before marking the client active, and sometimes select the wrong plan tier default.

TOOLS OR SYSTEMS INVOLVED
Our internal CRM and Stripe for payment processing.

Break the task into numbered steps, but for each step, state what a correct outcome looks like before moving to the next step — not just the action to take, but how the person doing it would know it worked. Mark clearly which steps are pure mechanical execution (no judgment needed, same action every time) versus which steps require a real decision (something depends on a variable circumstance), and for every decision step, state the actual criteria for making that call rather than leaving it to instinct — an SOP that says "use your judgment" at a step has usually just failed to do the actual work of specifying the decision rule. For every item in the common-mistakes list, find the step where that mistake would actually occur and add a specific recovery instruction right at that step — what to do if it's caught immediately versus what to do if it's discovered later, since the two often require different fixes. Assume the person following this SOP has never done the task before and cannot ask me questions in the moment — if a step assumes context that isn't stated in the SOP itself, add it rather than assuming it's obvious. Note explicitly which step, if skipped or rushed, would cause the most damage, so a time-pressured reader knows exactly where not to cut corners.

WHAT NOT TO DO
Do not write a step that says "use your best judgment" without specifying the actual decision criteria. Do not omit recovery instructions for a known common mistake just because it seems obvious to you.

OUTPUT FORMAT
Numbered steps: action, expected outcome/how to verify it worked, mechanical or judgment-required (with criteria if judgment), recovery instruction if this is a step where a listed mistake commonly occurs. End with one line flagging the highest-stakes step.