Certain aspects of the present disclosure provide techniques for validation rules for message transmission occasions. In some cases, a user equipment (UE) may select a random access message transmission occasion for a preamble and a payload of a random access message, wherein the random access message transmission occasion comprises a preamble occasion and a payload occasion, select a preamble sequence for the preamble to transmit in the preamble occasion of the random access message transmission occasion of a two-step random access channel (RACH) procedure, select at least one resource unit (RU) for transmitting the payload in the payload occasion, validate the selected random access message transmission occasion based on one or more criteria, and transmit the preamble sequence and the payload in the selected message transmission occasion if the selected random access message transmission occasion is validated.