Save Platform Credentials

Save credentials for non-OAuth platforms.

Body: shiprocket: { "email": "...", "password": "..." } payu: { "merchant_key": "...", "merchant_salt": "...", "environment": "production" } google_analytics: { "property_id": "..." } temple (TeraCart): { "api_key": "tk_live_...", "store_domain": "shop.example.com" (optional), "webhook_secret": "whsec_..." (optional), "base_url": (optional, TeraCart's own host only) } stripe: { "api_key": "rk_live_..." } (a restricted key that can read charges; never a secret key)