Please use the Onvif camera app topic for your questions, as mentioned at the app page @ homey.app store.
This way you reach the developer and fellow app users much better.
.
About
I’ve two Reolink cams, one has the same problem you mentioned, because it has no webserver to provide for the pictures.
You can test it in a browser, by copying the URL mentioned at cam Settings > Onvif Snapshot URL , like this one from my cam:
In these cases, you’ll need a specific app written for your cam brand/type.
.
Test tool:
