ChatGPT connects to MCP servers with OAuth or with no authentication: it cannot send an API key. Our server supports OAuth, so you sign in to your developer account and choose which key ChatGPT acts as. Checked against OpenAI's own pages on 24 October 2026.

Custom MCP server (plugins)

OpenAI's help centre says custom MCP servers with full MCP support are available to ChatGPT Business and Enterprise or Edu workspaces on the web, and that Pro users can connect custom servers with read and fetch permissions. All our tools are read-only. Business workspaces need an admin or owner to create and publish; Enterprise and Edu admins can give members the Create plugins with MCPs permission.

Go to Plugins (chatgpt.com/plugins).
Choose +, then Add custom MCP server.
Enter the name "Rally & Roam" and, under Connection, the server URL https://rallyroam.co.uk/mcp.
Choose OAuth for authentication. ChatGPT finds our OAuth settings itself from the server.
Read the risk warning and choose I understand and want to continue, then Create as a plugin.
Review the tools it found, then install the plugin.
You are sent to Rally & Roam to sign in and pick a key. Choose Allow.
In a conversation, type @ and pick Rally & Roam.

Every tool declares readOnlyHint: true, so ChatGPT treats them as read actions. After a workspace admin publishes the plugin, ChatGPT uses a snapshot of the tool list: if we add tools, choose Refresh to see them.

GPT Actions

OpenAI is retiring custom GPTs on 11 December 2026 (11 February 2027 for Enterprise workspaces with an approved deferral), and custom actions do not move to plugins. Prefer the MCP server above. Until then, you can add the API to a GPT you build:

In the GPT editor, open Configure, then Actions, then Create new action.
Choose Import from URL and enter https://rallyroam.co.uk/partner-api/v1/openapi.json. That file is an export of this reference in the format GPT Actions reads; you can also download it.
Under Authentication, choose API key, then Bearer, and paste a key. Use a test key while you try it.
Enter our privacy policy address, https://rallyroam.co.uk/de/api-privacy, which public GPTs need.
Use Test next to an action, for example listOrSearchClubs.

Actions have their own limits: summaries over 300 characters are cut, answers must be under 100,000 characters (use per_page to keep lists short), and each call must finish within 45 seconds.

Sources: help.openai.com articles 12584461 (custom MCP servers), 9442513 (actions in GPTs) and 20001519 (custom GPT retirement), and developers.openai.com pages on plugins, authentication and actions.

ChatGPT verbinden | Entwicklercenter