When I reached Lvl 5 (unlocking 2nd level spells) with my Ranger the dndbeyond page showed I could cast it at a 2nd level. But the description does not mention the effect at 2nd level.
It is also not mentioned in the general spell description of the game rules. If the effect on lvl 2 is the same as on lvl1, should it not make more sence to not be able to cast it at lvl 2?

You can upcast spells even if they don't have a mechanical benefit of being upcast. Say you were out of 1st level slots, you can still cast Hunter's Mark, you would just have to use a higher level slot.

You can always use a higher level spell to cast a lower level spell, even if it provides no additional effect. This allows your ranger to still be able to cast Hunter's Mark at all, if they run out of first-level spell slots but would find casting Hunter's Mark again more useful than casting their second level spell(s).

got it! much appreciated!