Error Endpoint auth data not present when using a service connection inside an Azure Custom Task

I have an Azure Custom task in which I want to read secrets from a key vault. In order to authenticate against the KV, I have added a service connection in the pipeline's project. I know that name of the service connection in advanced and I want to use it directly without adding a new input to the custom task.

What I tried is this code:

const spId = tl.getEndpointAuthorizationParameter(serviceConnectionName, "serviceprincipalid", false);
const spKey = tl.getEndpointAuthorizationParameter(serviceConnectionName, "serviceprincipalkey", true);
const tenantId = tl.getEndpointAuthorizationParameter(serviceConnectionName, "tenantid", false);

if (!spId || !spKey || !tenantId) 
{
    throw new Error(`Could not retrieve SC info of: ${serviceConnectionName}`);
}

const credential = new ClientSecretCredential(tenantId, spId, spKey);

// Connect to KV
const client = new SecretClient(kvUrl, credential);
const secret = await client.getSecret("my-secret");
const secretval = secret.value;

and in task.json I added a definition of the endpoint like this:

"endpoint": [
  {
    "name": "kv-sbx-sc",
    "type": "azurerm"
  }
]

when running the custom task in the pipeline I get this error:

Endpoint auth data not present: kv-sbx-sc

How can I fix it?