Manage error when indexing documents

Hello,
I want to know when a document is dismiss by Elasticsearch in case the mapping is configured with "dynamic : strict".
So, when i send a document who got an "unknow fields" in the mapping, Elasticsearch will dismiss him. How can i do for knowing that ? (without the api answer).
Is there a way with ingest pipeline, to ingest my malformed document in an other index ? (a special index, in wich they are just errors)

Your client will receive an error that you need to process.

How are you sending the data to Elasticsearch now?