Choose an API-compatible client, such as OpenCode or Codex, and install its desktop app or CLI. The regular ChatGPT app does not accept third-party API keys.
In CC Switch, select your client and add a Custom Configuration. Set the Base URL to https://api.apitokendeal.com/v1, then paste your full API key (starts with sk-) from the API Keys card below. Choose a model from the Model Catalog, save and enable the configuration, then restart your client.