Custom Code Workflow action to create a note on the current contact a year from the date they became a subscriber.

wf-action.js

const axios = require("axios");

exports.main = async (event, callback) => {
  // Pass in our private app token as a secret.
  // https://developers.hubspot.com/docs/api/workflows/custom-code-actions#secrets
  const privateAppToken = process.env.privateApp;

  // Pass in properties to your custom coded action.
  // https://developers.hubspot.com/docs/api/workflows/custom-code-actions#add-hubspot-properties-to-your-custom-code
  const contact_id = event.inputFields["contact_id"];
  const subscriber_date = parseInt(event.inputFields["subscriber_date"]);

  // add one year in epoch format to the subscriber date.
  const subscriber_date_plus_one_year = subscriber_date + (31556926 * 1000);
  // adding to subscriber date vs current date ensures even if the workflow timing isn't exact, the note for the date is.

  // We use the "Basic" create endpoint for notes. As documented here: https://developers.hubspot.com/docs/api/crm/notes
  let url = "https://api.hubapi.com/crm/v3/objects/notes";

  // a properties object is a required parameter so we create the object, the timestamp is what date we want to tie this note to.
  // The note body is the actual message that will be visible in the contact record.
  const properties = {
    "hs_timestamp": subscriber_date_plus_one_year,
    "hs_note_body": "This user has been subscribed for 1 full year!"
  };

  /* On the overview tab we can see there's an association object we can pass when creating a new note. This enables us to associate 
  the note to a specific contact. The associationTypeId can be retrieved via the associations API.(https://developers.hubspot.com/docs/api/crm/associations)
  The id for notes to contacts we received from the API was 202.
  */
  const associations = [
    {
      "to": {
        "id": contact_id
      },
      "types": [
        {
          "associationCategory": "HUBSPOT_DEFINED",
          "associationTypeId": 202
        }
      ]
    }
  ];

  // Make our API call to create the note.

  axios
    .post(
      url,
      {
        "properties": properties,
        "associations": associations,
      },
      {
        "headers": {
          "Authorization": `Bearer ${privateAppToken}`,
          "Content-Type": "application/json",
        },
      }
    )
    .then((response) => {
      console.log(response.data);
      return response.data;
    })
    .catch(function (error) {
      console.log(error.toJSON());
    });
};