AP setup, no IP in guest WiFi

While the EAP225 AP is working well, the WDR4900 AP setup seems not yet optimal.
The DHCP IP lease works but there is no internet connection.
What part of the config shall I post for inspection?

Edit:
I have tried another smartphone and this one gets internet access. I checked the associated stations list and both devices were using the same network.

Conclude, it must be another kind of issue then misconfiguration of the AP.
But, on the other hand, I wonder why the connection to the private wifi is working without problems?
It's always the same 2.4GHz radio that is used (Generic MAC80211 802.11bgn).
Private wifi is OK, gast wifi no internet.
Any idea?