From the rent/Trade board posting rules sticky post:
"All New Threads must be Validated
When you create a new thread, it will not appear immediately on the Rent/trade board. Instead, it first goes into a Moderation Queue where it is reviewed both for correct title and content. If the posting meets all R/T board requirements, the thread is validated and then appears on the board for others to see. If it fails validation, it is removed from the Moderation Queue and does not appear on the R/T board.
Please allow up to 24 hours for a thread to be validated. If after that time it has not appeared, then it has failed Validation. You need to review all posting requirements and correct whatever caused your thread to fail validation, and then create a new thread posting."