curl -X POST https://api.relayer.fi/v1/action/builders/crosschain-bridge \
  -H "Authorization: ApiKey $RELAYER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "fromChain": "base",
    "toChain":   "polygon",
    "token":     "USDC",
    "amount":    "100"
  }'

{
  "success": true,
  "metadata": {}
}