This script looks at the "referrer" property associated with the contact that has just converted and then leverages the CRM Search APi to find the matching contact with that specific "referrer ID". It then uses the CRM API to update the contacts "recent referral date" and "total referral" properties.

referralProgramAttribution-v2.js

const hubspot = require('@hubspot/api-client');

exports.main = (event, callback) => {

  const hubspotClient = new hubspot.Client({
    apiKey: process.env.HAPIKEY
  });
  
  //1) Get the enrolled deal - referrer_id property value
  hubspotClient.crm.contacts.basicApi.getById(event.object.objectId, ["referrer"])
    .then(results => {
      let referrer = results.body.properties.referrer; //contact Referrer ID
  
     console.log(referrer);
    
   //2) Search for the contact using the deals referrer_id and update
    const filter = { propertyName: 'referrer_id', operator: 'EQ', value: referrer }
    const filterGroup = { filters: [filter] }
    const sort = JSON.stringify({ propertyName: 'referrer_id', direction: 'DESCENDING' })
    const properties = ['referrer_id', 'total_referrals', 'firstname', 'lastname', 'email']
    const limit = 100
    const after = 0

    const publicObjectSearchRequest = {
        filterGroups: [filterGroup],
        sorts: [sort],
        properties,
        limit,
        after,
    }

 	hubspotClient.crm.contacts.searchApi.doSearch(publicObjectSearchRequest).then(results =>{

      	 let contactId = results.body.results[0].id;
      	 let referred_by = results.body.results[0].properties.email
      
         let totalReferrals = 0;
         if(results.body.results[0].properties.total_referrals === null || results.body.results[0].properties.total_referrals === undefined || results.body.results[0].properties.total_referrals === ""){
           totalReferrals = 0;
         }else{
           totalReferrals = parseInt(results.body.results[0].properties.total_referrals)
         }
      
         let totalReferralsUpdated = totalReferrals + 1;
      
      	var d = new Date();
      	d.setUTCHours(0,0,0,0);
      
         hubspotClient.crm.contacts.basicApi.update(contactId, {"properties":{"total_referrals": totalReferralsUpdated, "recent_referral_date": d}});
      
      	 callback({
        	outputFields: {
        	  reffered_by: referred_by
       	 	}
      	});
      
    });
  });
}   

referralProgramAttribution-v3.js

const hubspot = require('@hubspot/api-client');

exports.main = (event, callback) => {
    const hubspotClient = new hubspot.Client({
        apiKey: process.env.HAPIKEY
    });

    const referrer = event.inputFields['referrer'];
    console.log("REFERRED ID: " + referrer);

    //2) Search for the contact using the deals referrer_id and update
    const filter = {
        propertyName: 'referrer_id',
        operator: 'EQ',
        value: referrer
    }
    const filterGroup = {
        filters: [filter]
    }
    const sort = JSON.stringify({
        propertyName: 'referrer_id',
        direction: 'DESCENDING'
    })
    const properties = ['referrer_id', 'total_referrals', 'firstname', 'lastname', 'email']
    const limit = 100
    const after = 0

    const publicObjectSearchRequest = {
        filterGroups: [filterGroup],
        sorts: [sort],
        properties,
        limit,
        after,
    }

    hubspotClient.crm.contacts.searchApi.doSearch(publicObjectSearchRequest).then(results => {

        let contactId = results.body.results[0].id;
        let referrer_email = results.body.results[0].properties.email
        let totalReferrals = 0;

        if (results.body.results[0].properties.total_referrals === null || results.body.results[0].properties.total_referrals === undefined || results.body.results[0].properties.total_referrals === "") {
            totalReferrals = 0;
        } else {
            totalReferrals = parseInt(results.body.results[0].properties.total_referrals)
        }

        let totalReferralsUpdated = totalReferrals + 1;
      
        var d = new Date();
        d.setUTCHours(0, 0, 0, 0);
      
      	//Update Referred Contact      	
        hubspotClient.crm.contacts.basicApi.update(event.object.objectId, {
            "properties": {
                "referred_by": referrer_email
            }
        })
      
		//Update Referring Contact      	
        hubspotClient.crm.contacts.basicApi.update(contactId, {
            "properties": {
                "total_referrals": totalReferralsUpdated,
                "recent_referral_date": d
            }
        })
    });
}

referralProgramAttribution.js

const hubspot = require('@hubspot/api-client');

exports.main = (event, callback) => {

  const hubspotClient = new hubspot.Client({
    apiKey: process.env.HAPIKEY
  });
  
  //1) Get the enrolled deal - referrer_id property value
  hubspotClient.crm.contacts.basicApi.getById(event.object.objectId, ["referrer"])
    .then(results => {
      let referrer = results.body.properties.referrer; //contact Referrer ID
  
   //2) Search for the contact using the deals referrer_id and update
    const filter = { propertyName: 'referrer_id', operator: 'EQ', value: referrer }
    const filterGroup = { filters: [filter] }
    const sort = JSON.stringify({ propertyName: 'referrer_id', direction: 'DESCENDING' })
    const properties = ['referrer_id', 'total_referrals', 'firstname', 'lastname']
    const limit = 100
    const after = 0

    const publicObjectSearchRequest = {
        filterGroups: [filterGroup],
        sorts: [sort],
        properties,
        limit,
        after,
    }

 	hubspotClient.crm.contacts.searchApi.doSearch(publicObjectSearchRequest).then(results =>{
         let contactId = results.body.results[0].id;
         let totalReferrals = 0;
         if(results.body.results[0].properties.total_referrals === null || results.body.results[0].properties.total_referrals === undefined || results.body.results[0].properties.total_referrals === ""){
           totalReferrals = 0;
         }else{
           totalReferrals = parseInt(results.body.results[0].properties.total_referrals)
         }
      
         let totalReferralsUpdated = totalReferrals + 1;
      
      	var d = new Date();
      	d.setUTCHours(0,0,0,0);
      
         hubspotClient.crm.contacts.basicApi.update(contactId, {"properties":{"total_referrals": totalReferralsUpdated, "recent_referral_date": d}});
    });
  });
}   

@jyejamesdisisto, your error stack reveals that you're getting an API authentication error. Please note that you need to name your secret HAPIKEY and not PrivateApp_AccessToken in this action (it differs from the first action in that way)