In the letter written to his last deputy, Imam Mehdi (a) said that anyone claiming to meet him during Major occultation before Sufyani's advent is a liar. But there are reports of various people meeting him, so how can these be reconciled?
It means that people should not publicly claim to be in contact with Imam Mahdi (A) and use that as a grounds for their authority over people. It should also not be used as a justification for telling people what to do (for instance, telling people to change the shari'ah, or to give them money, or to follow a certain military leader, or to do anything else, because they say that this is what Imam Mahdi told them).
It is possible to meet Imam Mahdi (A) during the occultation and gain guidance or assistance, but this is a private matter, and it is between the individual and Allah whether or not that person truly met Imam Mahdi (A) or not.