That day you kept your word - test question

That day you kept your word - test question

Hello, based on the lesson, it would appear that an article or a possessive adjective is either required or at least optional but i was marked incorrect for the answer:

Ce jour-là tu as retenu la parole.

and the only accepted answer was:

Ce jour-là tu as retenu parole.

Could someone advise on why the former is incorrect? Is it idiomatic?

thanks