When did appeals become possible in Roman legal procedure?

In the context of Roman legal procedure, a formal system of appeal became possible under the cognitio extraordinaria.1

This procedure, which operated during the post-Classical period, marked a significant shift in the Roman legal system. Unlike the earlier legis actiones and the formulary system—where trials were divided into two stages and relied on a contractual element—the cognitio extraordinaria placed greater power directly in the hands of the magistrate and the courts. Under this later system, the state took responsibility for issuing summons, conducting the trial, executing the sentence, and providing a mechanism for appeal, reflecting a move toward the administration of justice seen in modern states.12