Create Wallboard from API REST calls

hello Darwood 

I think you have done most of the hard work to get the authentication and connection done

Now for Web Activity Output Handling
• Use a Set Variable activity to capture the Web Activity response
• Configure the variable to store the complete JSON output

Create Copy Data Activity Setup
• Create a dummy source query using a Fabric Datawarehouse connection
• Use the “Additional Columns” section in the source to define your output schema
• Configure the destination as the Lakehouse Files section
• Map the fields from your variable to the destination columns

check this discussion it will be helpful 

https://community.fabric.microsoft.com/t5/Data-Pipeline/Writing-Pipeline-Output-to-JSON-file-in-Lakehouse/m-p/4117453

If this helps. Please accept the solution 

Thanks