A post-only rejection can be the correct result

An order is rejected and it feels like a platform problem. With a post-only order, rejection can be the protection you asked for.

Post-only means the order should rest on the book as a maker order. If it would match immediately, it is rejected instead of becoming a taker trade.

Write the execution intent first

Before submitting, decide whether you are adding liquidity or trying to trade immediately. Post-only is an instruction about that intent, not a cheaper version of an immediate order.

Do not silently resubmit a rejected post-only order as a normal order. That changes the execution path and the fee or price assumptions in your plan.

Check the current spread

Use the best bid and ask at the moment of submission. A buy at or above the lowest ask, or a sell at or below the highest bid, is marketable and can violate the post-only requirement.

A quote that rested a minute ago can cross after another order moves the book. The rejection may describe the new spread, not a broken order.

Log the rejection as process data

Save the side, price, size, timestamp, visible spread, and book hash. Note whether you would rather revise the price, wait for the spread to move, or accept a taker execution.

That record keeps a maker strategy separate from a later decision to cross the book. It also prevents a rejected attempt from being counted as exposure.

The useful question is not whether the order was rejected. It is whether the final action still matched the execution intent, price, and risk budget you started with.

Further reading: Order lifecycle · Prices and order books · Current fees.

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