Can we get an update from devs on this issue please?
I have the same problem: essentially, how to set a Lookup value in a dropbox listbox control, when creating a child in a parent-child relationship. This is using Sharepoint lists with lookup columns.
In my case I'm selecting the related record in a gallery, then adding a new child record, using a button to navigate to another screen with an edit form. While PowerApps figures out the possible Lookup relationships fine (i.e. populates the dropdown list), having to manually select the parent (i.e. the Lookup value) is incredibly tedious and redundant when the parent is already selected on the first screen.
How would I reference a parent value of the previous view screen? I tried context variables (see below) but that didn't work. The error came up with the message: "The requested operation is invalid. Server Response: A value must be provided for item.
For the testing I am displaying the context variables "paramCustomer" and "paramID", per the screenshot below, so they seem to be storing the correct values, but somehow the way I am pulling them into the default configuration must contain a syntax error of some kind.