Your serverless runtime environment might have failed to start because the region entered was incorrect. Once a region is selected, you can't change it. You need to delete the serverless runtime environment and then recreate it using the correct region.

A network security group is automatically created and attached to the region. When you change regions, the network security group no longer matches the new region and the environment fails to start. The only way to correct this is by deleting the environment and creating a new one.