I can not reach my nexclud Server from my iphone app. From Browser it does work without Problems and every other client ( Mac, Linux) is able to reach my host, too.
But on the Iphone App i always got the error : Verbindungsfehler : Fehlerhafte Anfrage
I have a possible solution to this issue, assuming that this issue happened while trying to access the server directly.
Similar to your situation, I was able to connect to the server through the same iOS device using a browser and other devices on my network.
The solution was to go into that device’s iOS settings, scroll down to find the nextcloud app and open its settings. Under “ALLOW NEXTCLOUD TO ACCESS”, enable “Local Network”.