For the last two years this Russian disinformation narrative has claimed that the US has been blocking the aid to Al Rukban camp, as you can see here and here, when it was actually the Syrian army who was responsible for the blockade. According to the civil administration of the camp, "not a single civilian" used the corridor on the next day, "because of the uncertainty of their destination after exiting the corridors". According to some local opposition activists, many of them are unsure if they will be allowed to return to their homes or be sent instead to new camps under regime control. So Russian authorities and media started to claim that US-backed terrorist groups are preventing the civilians from leaving the place.
In reality, many of those refugees are linked to rebel factions and fear retaliation if they abandon the camp. The US position is to encourage residents to stay, but says it won't impede the movement of those who want to leave. According to a journalist reporting on the ground for The Guardian, smugglers are indeed requesting huge sums of money to those who want to leave, but to take them beyond the Syrian government areas.