Does the vow to donate money remain obligatory for someone who vowed to donate money but was unable to secure the full amount before traveling, and how can this vow be fulfilled?

If one vows a vow of obedience, it becomes obligatory to fulfill it. A vow to give charity is one such vow. If both of you are unable to fulfill it, it remains a debt upon your consciences until you are able to do so. You must repay the amount for the months you did not pay, and a vow does not avert anything decreed by Allah.