Use Azure Data Factory with a Copy Data activity to ingest the JSON data from the REST API and store it in Azure Blob Storage. Then, use a Data Flow activity to flatten the JSON data and store it in Azure Data Lake Storage Gen2.

Use Azure Event Hubs to capture the JSON data from the REST API, and then use Azure Stream Analytics to process the data and store it in Azure Data Lake Storage Gen2.

Use Azure Logic Apps to trigger a workflow for each JSON object in the REST API, and then use a custom connector to flatten the JSON data and store it in Azure Data Lake Storage Gen2.

Use Azure Databricks to run a custom script that ingests the JSON data from the REST API, flattens the nested structures, and stores the transformed data in Azure Data Lake Storage Gen2.