Even if you have a lot of workers at your Home station, some of them can be busy at other factories at the moment.
There are several ways how to start the production at the needed factory:
1. Wait until the workers are available - to check the number of available workers, tap on any of the workers' houses.
2. Provide more housing for your workers - you can buy residential buildings at the Market for coins.
3. Hire more workers with emeralds - click on the button Hire in the factory menu. Please note that the workers will stay with you for a limited period of time.
If you have any questions, please contact us and we will help :)