Given:

class Game(models.Model):
    rengo_black_team = models.ManyToManyField(Player)

class OpenChallenge(CommonChallenge):
    rengo_black_team = models.ManyToManyField(Player)
    game = models.ForeignKey(Game, on_delete=models.CASCADE)

This OpenChallenge method code works:

for p in self.rengo_black_team.all():
    self.game.rengo_black_team.add(p)
    

But this code does not:

    self.game.rengo_black_team.add([x for x in self.rengo_black_team.all()])
    

Based on the last example in the docs ,

>>> john = Author.objects.create(name="John")
>>> paul = Author.objects.create(name="Paul")
>>> george = Author.objects.create(name="George")
>>> ringo = Author.objects.create(name="Ringo")
>>> entry.authors.add(john, paul, george, ringo)

it seems like my example should work, but I get

"Field 'id' expected a number but got [<Player: anoek>]"