Need assistance with a JSON data structure

Hello Makers, I'm looking to construct a JSON string for an API call using an HTTP module.

I'm currently utilizing a Create JSON module, feeding it fields from preceding steps.

This works fine for basic elements, but I'm having trouble understanding the required data structure for an array field named "accommodation", as shown below.

Here's an example of the desired structure:

"accommodation": [
           {
               "externalId":"HPO1",
               "libraryExternalId":"HOTELS",
               "arrivalDate":"2025-09-05",
               "departureDate":"2025-09-06",
               "comment":"A generous breakfast buffet is included"

           },

 {
               "externalId":"HPO2",
               "libraryExternalId":"HOTELS",
               "arrivalDate":"2025-09-06",
               "departureDate":"2025-09-07",
               "comment":"Dinner is included"

           }
       ],

The input for the accommodation field is a JSON string generated by an Aggregate to JSON module. Here's an example of that input:

[
{"comment":"1x DBL (B&B)","externalId":"recRGrW4ugkbvK8T3","arrivalDate":"2025-05-16","departureDate":"2025-05-17","libraryExternalId":"Hotels"},
{"comment":"1x DBL (B&B)","externalId":"rectZqonA40XLxT2C","arrivalDate":"2025-05-17","departureDate":"2025-05-18","libraryExternalId":"Hotels"}
]

What should the data structure within the Create JSON module look like to correctly process the input from the Aggregate JSON module?

Create JSON data structure:

image445×662 30 KB

Create JSON module configuration:

The current setup is producing a plain JSON string and resulting in API errors such as: "JSON parse error: Cannot construct instance of XXXX (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value"

Thanks for your assistance!