This custom coded action takes the most recent value from the record type in question then adds a value to that previous amount. Use this code for auto incrementing records.

auto increment a deal record using crm search api.js

var axios = require('axios');
const auth = 'Bearer ' + process.env.ADD_YOUR_SECRET_KEY_NAME_HERE;

exports.main = async (event, callback) => {
  
  var data = JSON.stringify({
    "filterGroups":[
      {
        "filters":[
          {
            "propertyName": "property_auto_incrementing",
            "operator": "HAS_PROPERTY"
          }
        ]
      }
    ],
    "sorts": [
      {
        "propertyName": "property_auto_incrementing",
        "direction": "DESCENDING"
      }
    ],
    "properties": [ "property_auto_incrementing" ]
  });
  
  // CHANGE DEAL TO THE OBJECT TYPE YOU'RE USING IN THE URL BELOW
  var config = {
    method: 'post',
    url: 'https://api.hubapi.com/crm/v3/objects/deals/search',
    headers: { 
      'content-type': 'application/json', 
      'Authorization': auth
    },
    data : data
  };

  axios(config)
  .then(function (response) {
    // console.log(JSON.stringify(response.data));
    
    let result = JSON.stringify(response.data);
    const obj = JSON.parse(result);    
    // console.log(obj);
    let most_recent_value = obj.results[0].properties.property_auto_incrementing;
    // CONVERT THE STRING TO NUMBER (MAY NOT BE NEEDED)
    let most_recent_value_num = Number(most_recent_value);
    
    // YOU CAN CHANGE THE AUTO INCREMENTING AMOUNT BELOW - AS NEEDED
    let next_value = most_recent_value_num + 1;
    
    callback({
      outputFields: {
        most_recent_value: most_recent_value,
        next_value: next_value
      }
    });
  })
  .catch(function (error) {
    console.log(error);
  });


  
}