During the day when the baby is being supervised by the parents it's okay for the baby to sleep or nap in the baby bouncer.
But a baby should not be allowed to sleep all night in a baby bouncer because the baby could potentially die when left unsupervised.
There have been a few babies that have died as a result of being left in the baby bouncer overnight to sleep but if you just want to let the baby nap or sleep during the day in the baby bouncer while you're watching the baby it's perfectly okay.
But if you cannot watch the baby longer than 20 minutes or so then it's best to remove the baby from the baby bouncer and place the baby in a baby bed, crib or bassinet or even in a playpen such as a pack and play playpen.
My babies would nap in the baby bouncer but if they were gonna sleep an hour or longer or I had to do something else while the baby is sleeping I would place them in a bassinet or their crib.