If you are facing this error when using the Postgresql database with OpenWebUI you can follow this to fix it.
InvalidRequestError: Could not reflect: requested table(s) not available in Engine(postgresql://chetan:***@installvirtual.postgres.database.azure.com/chetan): (document_chunk)
CREATE TABLE document_chunk ( id TEXT PRIMARY KEY, vector VECTOR(1536), collection_name TEXT NOT NULL, text TEXT, vmetadata JSONB );
I created this Table manually in the Postgresql database and then it worked.
Read Also: How to use PostgreSQL with OpenWebUI