Configuration of Sensor via it's website

I cannot access the config website of the sensor although i got the correct ip adress from my fritz box. But: I have a repeater and the sensor connected via the repeater to my box.
How can I access the config page?

Is the sensor in the same network than the device you use to access the config website?
And is the sensor NOT in a guest wifi? Those are normally blocking the access between devices.

I configured a guest access for my iot devices.

So you may need to enable temporarily that these devices can “see” each other.