Variable to Parts of JSON Request Body

The Google Places API (New) seems to allow looking up places for a single LatLon pair at a time. Here’s a valid request body:

{
"includedTypes": ["spa"],
"maxResultCount": 10,
"locationRestriction": {
"circle": {
"center": {
"latitude": 40.4436121,
"longitude": -104.984106},
"radius": 5000.0
}
}
}

I’m hoping to produce a workflow that loops over a list of latlons to concatenate the results at the end, but having trouble getting the JSON Request Body constructed correctly. Up to the “Column Combiner” node in the image below, I can get the following:

{   "includedTypes": ["spa"],   "maxResultCount": 10,   "locationRestriction":{
"circle" : {
"center" : {
"latitude" : 40.4436121,
"longitude" : -104.984106
}
}
}

If I add the radius = 500.0 key/value pair in the Columns to JSON node, the radius appears in the wrong place:

{
"circle" : {
"center" : {
"latitude" : 40.4436121,
"longitude" :-104.984106,
"radius" : "500.0"
}
}
}

Appreciate any help!

Here is the draft workflow on Community Hub%20API~q6qg2H-54sV-9Yrj/current-state).