That’ll be a problem regardless – if the client provides an idempotency-key but the server doesn’t use it, it’ll reprocess on retry. Under this spec, the client needs to check server docs to figure out if/when/how idempotency keys are used.

The weird part of calling them idempotency keys is that seperate requests will often fall in the same idempotent group.

EG: If traffic lights were controlled over HTTP, a pedestrian pressing the crossing button 20 times in a row would create 20 distinct requests which would need 20 distinct idempotency keys. But pressing the button once is the same as pressing it 20 times.