Formatting is not the same as fixing
Indentation makes JSON readable, but it does not decide whether a value should be a number, string, array, or object. Start with an untouched copy. The formatter should expose the structure before you change the model.
Read the error from the nearest stable point
When validation stops at a character, look just before it for a missing quote, comma, colon, or closing bracket. Errors often surface one token after the real mistake. Repair one issue, validate again, and avoid making several speculative edits at once.
Watch for valid data with the wrong meaning
A payload can be valid JSON and still be wrong for an API. Check quoted numbers, true and false values, null, duplicate-looking keys, date formats, and empty arrays. Compare the cleaned result with the contract or example expected by the receiving service.
Share a safe sample
Before pasting JSON into a ticket or chat, replace tokens, email addresses, identifiers, and customer data. Keep the key shape and data types so the sample still reproduces the problem.