Open Customize → MCP (or edit ~/.cursor/mcp.json). Add a custom server named PostWing, paste the URL, leave OAuth blank, then approve access.
MCP server URL
https://postwing.io/api/mcpmcp.json example
{
"mcpServers": {
"postwing": {
"url": "https://postwing.io/api/mcp"
}
}
}