| title: 'The key `<your key>` under "env" in `next.config.js` is not allowed.' | |
| ## Why This Error Occurred | |
| Next.js configures internal variables for replacement itself. `NEXT_RUNTIME` along with variables starting with `__` or `NODE_` are currently internal, for this reason they are not allowed as values for `env` in `next.config.js` | |
| ## Possible Ways to Fix It | |
| Rename the specified key so that it does not start with `__` or `NODE_`, or pick another name for `NEXT_RUNTIME`. | |