Actually, you are putting everyting in the same parameters.
But in this case, you need to have an object {} for each line
Example:
“calculation_details”:[
{“description”:<description_value>“,“amount”:”<amount_value>“},{“description”:<description_value>”,“amount”:“<amount_value>”}]
this mean 2 line.
But if you have dynamic data that will change on how many item you will have, you will need to use a more complex option
You will set in API Connector: “calculation_details”:[<calc_detailss],
And in the workflow, for this part, you will use :format as text.
Please read this post for a few informations about that