Filtering/Setting a lookup column

[entertain89]

Ok a bit of background, I have exactly what I want to accomplish setup and working in PowerAutomate already. When an item is created on List A a related item is created on List B. I'm carrying over a bunch of column values from the triggering item on list A and setting them in fields on list B.

Now I need to make that same functionality in PowerApps as there are occasions where creating items on list B needs to be done manually (without first creating a new item on List A thereby triggering the workflow). This is the PowerAutomate step for creating the item on List B (with some org specific censoring done).

So I am customizing the List A form in PowerApps to add a second form with the above fields on it for creating a new item on list B. I need to carry over one value (List A item ID) from an existing (currently being viewed by the user) entry over to two fields ("Job Number ID" and "Associated ID Hidden") in the new List B item.

"Associated ID Hidden" was easy enough to set to the list A item ID as it's a single line of text type column. I'm really struggling to set "Job Number ID" though as it's a combobox tied to a lookup column (It lookups info from List A). The complicating factor here is Lists A & B are huge (~15,000 items) so I need to filter them to make them useable. I already know the list item ID number I want to set in Job Number ID (as it's the same as Associated ID Hidden) but PowerApps won't you let you explicitly set a lookup field value (I tried). 

So I need to narrow down what is returned to make the field useable.  I've tried all manner of LookUp, Filter, Search, etc functions in the Items property. I just can't seem to write a query in such a way that I get any results returned. Lots of my attempts don't show any errors in PowerApps but they also fail to return any records in the combobox.

I essentially want to tell the combobox only return "Job Number ID" record that matches "Associated ID Hidden".

Since I know the item ID I'm looking for out of the list the lookup field references this seems like it should be easy but I'm thoroughly stuck. 

TL;DR help me write a filter/lookup query for a combobox that takes a known list item ID # and returns only that corresponding record.

[entertain89]

Ok So I'm taking a different approach to setting this. 

I've got the following set in the update property of the job number data card: 

{'@odata.type' : "#Microsoft.Azure.Connectors.SharePoint.SPListExpandedReference", Id: myID, Value: jobNum}

There are no errors produced from the code itself but when I try to submit the form I get an error about the patch function:

Is calling update like this technically using patch? what can I change to fix this?