Can a ranger pick two humanoid races as their favored enemy at level 1, and then two more humanoid races at level 6?

Can a ranger pick two humanoid races as their favored enemy at level 1, and then two more humanoid races at level 6 or level 14?

My reading of the Favored Foe feature is that any time the ranger chooses a favored enemy, be it at Level 1, 6 or 14, the ranger may alternately choose two humanoid races instead of one non-humanoid creature type. However, D&D Beyond does not allow a player to choose two more humanoid races at level 6 or 14 if they have previously chosen two humanoid races at level 1 or 6.

Is my interpretation of the Favored Foe feature incorrect, or is D&D Beyond’s implementation incorrect?

Note: My question is similar, but not a duplicate, to this one. That question is about a scenario where a ranger chooses a non-humanoid creature type as their favored enemy at level 1, and then wants to choose two humanoid races at level 6. My question is about a ranger who chooses two humanoid races at level 1, and wants to choose two more humanoid races at level 6.