Explanation
A DataRaptor Transform can be used to transform data from one format to another, such as JSON, XML, or CSV. The developer can specify the input and output paths for each field in the Transform tab. The developer can also use formulas to manipulate data in the Formula tab1. To transform contact data into a JSON array, the developer can use either of these methods:
Use a formula LIST(Contact), and add the output of the formula as the input in the Transform tab. This will create a list of contact objects from the input JSON and output it as a JSON array.
Set the Input JSON Path as Contact, the Output JSON Path as Contact, and the Output Data Type as List. This will output each contact object as an element of a JSON array.

Explanation
The Upsert Key checkbox indicates that the field is used as a key for upserting records. The Is Required for Upsert checkbox indicates that the field is mandatory for upserting records. The developer needs to check both checkboxes on the Account Id field to update the Account status only if the Account record already exists.
Otherwise, a new account will be created.

Explanation
The Repeatable Mode property on the data table elements allows the developer to display multiple records in a single data table. The Repeat Records feature on the FlexCard Setup tab is used to display multiple FlexCards for each record in a data source. The Record Looping feature on the data table elements is used to iterate over a list of records and perform actions on each record. The Overwrite Target for all Null input checkbox on the Account id field is used to overwrite the existing value in the target object with null if the input value is null.