In Belgium, it is prohibited to operate games of chance if you do not have the required licence from the Gaming Commission (GC). This is based on Article 4(1) of the Gambling Act.
Article 3(1) of the Gambling Act defines certain activities which, under certain conditions, are not games of chance. These are card or party games which are played outside gambling establishments class I (casinos) and class II (slot machine halls), with the exception of card or party games which are played in gambling establishments class III (cafés), using a device which requires only a very limited stake and which can only provide the player with a material advantage of limited value.
The other conditions must still be determined by royal decree. The Gambling Act grants this power only to the King. The GC does not have the power to determine these conditions itself. Therefore, the GC cannot offer any advice in response to your question.
The only thing we can recommend is not to organise an activity if you are in doubt about its legality.