You can set mission submissions to be automatically approved in the mission maker. This is a feature is best used for low value or basic missions, and will only approve a submission if the ambassador has followed the mission instructions.
To set automatic approvals on in the mission maker, go to the 'Action' tab and scroll dow to 'Action Type Settings'. If it's not already, open the 'Advanced Settings' accordion. Switch on the 'Automatic mission approval' button, and submissions will automatically be approved for that mission.
Once submissions are set to automatic approval, your ambassadors will receive their reward as soon as they submit to the mission, provided they have correctly followed instructions. Although this feature prevents you from having to go through hundreds of submissions, it's not recommended to use for high-value or content-heavy missions, as you will want to go through and approve these submissions yourself.