psycopg2 giving foreign key error even though we have a foreign key and required data in the DB

Question

We are using psycopg2-binary==2.8.6

Am trying to insert huge data into my table (staging_schema.table_name) we do exist foreign key and all necessary data, However it's throwing an error:

Error: insert or update on table "table_name" violates foreign key constraint "test_table_id_fkey"

Key (api_id)=(487717270)

is not present in table "test_table"

buffer = StringIO()
api_trx_stg_df.to_csv(buffer,index=False, header=False)
buffer.seek(0)   
cursor = utils_dict['psycopg2_connection'].cursor()

try:
    cursor.copy_from(buffer, 'staging_schema.table_name', sep=",",columns=api_trx_stg_df.columns)
    utils_dict['psycopg2_connection'].commit()
except (Exception, psycopg2.DatabaseError) as error:
    
    logging.info("Error: %s" % error)
    utils_dict['psycopg2_connection'].rollback()
    cursor.close()
    return 1
logging.info("copy_from_stringio() has done")
cursor.close()

When am trying same with the to_sql(), it's working as expected but we are dealing huge data, so I have moved it to copy_from.

When am trying same with the to_sql() it's working as expected but we are dealing huge data so I have moved it to copy_from. How can we fix this ?