Learn Farsi: ما باید تاریخ پرواز را هماهنگ می‌کردیم. - We should have coordinated the date of the flight.

To express a past obligation (something you should have done), Farsi uses the unchanging word باید followed by the Past Continuous tense of the main verb. Here, باید pairs with می‌کردیم. Even though it literally translates closer to "we must... we were coordinating", this specific combination is how Farsi says "we should have coordinated".

Why doesn't باید have a personal ending to match ما (we)?

باید is a fixed (invariant) word, meaning it never changes form to match the subject. You use the exact same word باید whether you are saying "I should have," "she should have," or "we should have." Only the main verb at the end of the sentence (می‌کردیم) conjugates to show who is doing the action.

How is the verb هماهنگ می‌کردیم built?

It is the past continuous form of the compound verb هماهنگ کردن (to coordinate). هماهنگ means "harmonious" or "coordinated," and کردن means "to do/make." To form the past continuous, you leave هماهنگ alone, add the continuous prefix می‌ to the past stem کرد, and attach the "we" ending ـیم (-im).

Why does را come after پرواز instead of right after تاریخ (date)?

را marks the entire definite direct object. In this sentence, the direct object is the whole phrase "the date of the flight" (). Because and are linked together by the hidden vowel sound (-e), they act as a single unit. Therefore, gets placed at the very end of the phrase.