Question about i-tec USB C to

Hi digitec team, I have the:Asus ROG Strix GL703 GM (https://www.digitec.ch/de/s1/product/asus-rog-strix-gl703gm-ee014t-scar-edition-1730-full-hd-intel-core-i7-8750h-16gb-256gb-1000gb-ssd-ss-7953977) and want to use two external monitors with this adapter. Somehow this does not seem to work. I always get an error message saying that the adapter is probably not supported. What is the problem? The connection on the Asus should support the adapter...?