New Index S2 - Unable to find WiFi

Are there also 2.4ghz networks available? Don't know if 5ghz is supported 

yes. i am aware 5g isnt supported, there are available 2.4g networks with WPA2 security and Googles DNS.

What's about the length of WiFi-SSID? In one post it was mentioned, that number of characters could be an issue.

Did you consider this? 

Yes I mean I considered it very briefly seeing as people in the same thread were able to connect with longer SSIDs, that it would be ridiculously moronic for developers to place such a restriction on SSIDs given that almost every SSID you will find will be longer and contain certain non letter characters, and also on the basis that there is at least one WiFi network within range that fits this and it doesn't even detect that one.

i found a problem with my wlan.

if in the password is "!" (TKIP/AES) WPA2-Personal then the connection failed.

I am struggling to get the device to connect to my app. I try to press the Reset button but it doesnt really work until 5 minutes later after trying it all different ways.

My situation does not contain any of the issues listed in the comments.

I believe my issue may be something to do with the fact that I am running a dual band router with seperate 2.4g and 5g bands. However, even if I specify the 2.4g band, and ensure my linked phone is also on the 2.4g band, the device fails. All the technical support team has been able to do for me is send me on a repeated loop of diagnostic tests without providing a solution.

Even without that, this product was not advertised as being only compatible with 2.4g networks, and having such restrictive connectivity. Given most people are running 5g or higher networks, I would expect a compatibility issue such as this to be made very clear.

I have returned the product for a full refund on the above grounds.