Not in error" is a phrase that describes an action or decision that has been made correctly and accurately. There are several synonyms that can be used to describe this concept such as "spot-on", "flawless", and "accurate". Other words that can be used to convey a similar meaning include "correct", "right", and "infallible". These words can be used in various contexts, such as a scientific experiment, a legal decision, or a mathematical equation, to describe something that has been done correctly and without errors. Using synonyms for "not in error" helps to convey accuracy and precision, and can help to instill confidence in the outcome of the action or decision.