I have been working a lot with Azure Logic Apps over the past month.  Since I am new to Logic Apps, I often run into silly issues that turn out to trivial to fix.  This is one of them. 

I was working with the HTTP Rest API shape to try to call a custom API, actually trying to call the Azure REST API to do an action on another Logic App – but more on that later.

I was setting Content Type and Authorization inside the Headers file as shown below:

I kept receiving this error:

Unable to process template language expressions in action 'HTTP' inputs at line '1' and column '1234': 'Error reading string. Unexpected token: StartObject. Path 'headers.authentication'.'.

The fix was super simple.  I had not expanded the Show Advanced Options for this shape.  Once expanded, I see the Authorization is broken out from the other Headers.  I moved the Authorization section from the Headers to here and it worked as expected!

So note to self, is something does not work as expected try expanding the Advanced Options section of the shape to see if that might help.