From the ELM perspective it's worth checking the following the only other points I can add to assist with the HTTP API are as follows:
-All devices must be on the same network (either connected into a WiFi router or wired).
-Check to check if your PC’s firewall isn’t blocking communication so ELM isn’t turned off.
-It is advisable to give your ELM PC a static IP.
This should be all ELM’s HTTP API requires to be used.
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From your description, above it seems the IP address in Ctrl for iPad hasn't been defined for it to send command to ELM. (ELM doesn't support any kind of discovery for remote software / applications to find it).
If you head over to the Ctrl for iPad forum I’ve put together a post relating to connecting CFi to ELM to assist from the Ctrl for iPad perspective (+ a screen recording).
Hope this helps, feel free to add any comments on the Ctrl post if you require any assistance with the App.
Thanks,