Issue with OpenSearch index not retrieving joined table data via ingestion pipeline

I am currently utilizing OpenSearch Service (specifically OpenSearch Serverless) for indexing data from my application's tables. To manage the indexing process efficiently, I've set up an ingestion pipeline to connect to my table. Within this table, I've employed a join method to link two tables.

However, I've encountered an issue where the data from the joined table is not being retrieved in the OpenSearch index. Despite configuring the ingestion pipeline to index the connected tables, the joined table's data does not appear to be accessible via the OpenSearch endpoint.

Could you kindly provide guidance on how I can ensure that the joined table's data is properly indexed and retrievable through the OpenSearch endpoint?