How to set up GS1900 VLAN's using a non-Zyxel router?

I’m having trouble getting VLANs to work on my Zyxel GS1900-8.

In my test situation, the GS1900-8 has 2 ports connected:

• On port 1, it’s connected to my Asus router with (highly configurable) Fresh tomato firmware. I have 2 VLAN’s on the router; VLAN2 and VLAN3. Those VLANS works fine together with a Zyxel NAP102 WAP that's connected to this ASUS router.
• On port 4, my Windows10 laptop.

All works fine in the 'default' situation; if I configure the ASUS router to send untagged packages to port 1 of the Zyxel GS1900-8, because the GS1900-8 uses it’s default VLAN1 and has all ports in the ‘untagged’ section by default.  

Then I tried to set up VLANs by configuring:

• the ASUS router to send tagged VLAN2 and VLAN3 packages to the GS1900-8
• the GS1900-8 as follows:VLAN2 settings: port 1 (the Asus router) = ‘Tagged’, Trunk enabled, port 4 (my laptop) = untagged and Trunk disabled, all other ports=excluded.

This doesn't work; f.i. from my laptop on port 4, I can’t ping the ASUS router on port 1, when I would expect them to connect via VLAN2.

Have I misconfigured something? Or could it be possible that the packaged tagged by the ASUS router aren’t compatible with the GS1900-8? The ASUS router works fine with the Zyxel NAP102 though…