Set application environment variables in Coolify via the API

Steps

1. Create a bearer API token with write permission
2. For a single variable, POST /api/v1/applications/{uuid}/envs or PATCH .../envs/{env_uuid} to create/update one entry
3. For many variables at once, PATCH /api/v1/applications/{uuid}/envs/bulk with a JSON body: {"data": [{"key":..., "value":..., "is_preview":..., "is_literal":..., "is_multiline":..., "is_shown_once":...}]}
4. Redeploy the application (or rely on instant_deploy on next deploy) for changes to take effect in the running container
5. Use DELETE .../envs/{env_uuid} to remove a variable