Welcome to the forum and thanks for adding your profile picture. It helps build community! When you get a chance, please introduce yourself on this forum thread.
Please note that Aggregate is no longer being supported. Central is now the ODK server. The post below has for more details about the end-of-life for Aggregate.
Are you able to access your Aggregate from your web browser? I would also recommend checking the server logs for more information.
If possible, please consider using ODK Central. The easiest option is to support ODK by purchasing an ODK Cloud subscription. If you don't want to pay, and can set up everything on your own you can do that as well by following the installation documentation.