High-tier gateways, particularly those from the Apotheosis mod, are often hardcoded to look for "invader" data specific to the Overworld.
If you try to open these in a Mining Dimension or a Compact Machine , the mod may fail to resolve the entities and default to the "not enough space" error. Despite what the error message suggests, the problem
While you might have a 100x100 flat platform, the gateway checks for as well. Despite what the error message suggests
Despite what the error message suggests, the problem isn't always that your arena is too small. Developers of the mod have acknowledged that this specific error message is sometimes triggered by generic spawn failures. 1. Dimensional Restrictions (The "Invalid Dimension" Bug) particularly those from the Apotheosis mod
Gateway Imploded: Troubleshooting the "Not Enough Space" Error in Gateways to Eternity
Players have found that moving the same setup from a custom dimension back to the Overworld often solves the issue instantly. 2. Hidden Height Requirements (The Giant Problem)
One of the most common causes is attempting to run a gateway in a dimension it wasn't designed for.