Using custom bundler in safe-core-sdk

[nufailTanjiro]

How to use a custom or 3rd party bundler other than Pimlico in safe-core-sdk?

 const safe4337Pack = await Safe4337Pack.init({
    provider: STACKUP_BUNDLER_URL,
    signer: PRIVATE_KEY,
    bundlerUrl:
     <WANTED_TO_USE_CUSTOM_OR_STACKUP_BUNDLER_HERE>, //"https://api.pimlico.io/v1/sepolia/rpc?apikey=<API_KEY>",
    options: {
      safeAddress: "0xE4AaE32a17FCD6E703a5AfC8Da57CA7FBBD1288F",
    },
  });

I tried changing the bundler URL to Stackup's bundler. I get:

info: {
    requestUrl: 'https://api.stackup.sh/v1/node/9717a247d0024c41a2f85aa629a5fc4cdc4ca40196663e70643108642eda35c8',
    responseBody: '{"error":"invalid request: method namespace is not enabled"}',
    responseStatus: '400 Bad Request'
  },
  shortMessage: 'server response 400 Bad Request'

Has anyone tried using custom or any other bundler except PIMLICO?