Ajv nodejs schema validation: get value of custom field in case of error

Question

I have following nodeJs code

const Ajv = require('ajv');
const addFormats = require('ajv-formats');
const ajv = new Ajv({allErrors: true, allowUnionTypes: true});
addFormats(ajv);

// addKeyword for severityType ??

const schema  = {
  $schema: 'http://json-schema.org/draft-07/schema#',
  type: 'object',
  properties: {
    slices: {
      type: 'array',
      items: {
        type: 'object',
        properties: {
          personId: { type: 'string', severityType: 'error' },
          position: { type: 'string', severityType: 'error' },
          networkId: { type: 'string', severityType: 'warning' },
        },
        required: ['personId', 'position', 'networkId'],
      },
    },
  },
  required: ['slices'],
}

const data = {
  slices: [
    {
      personId: 55, // This should trigger the severityType 'error'
      position: null, // This should trigger the severityType 'error'
      networkId: null, // This should trigger the severityType 'warning'
    },
  ],
};

const validateSchema = (data, schema) => {
  const validate = ajv.compile(schema);
  const isValid = validate(data);
  if (validate.errors) {
    logger.error(`Validation errors: ${JSON.stringify(validate.errors)}`);
    logger.error(`severityType : //print severityType `);
  }
  return {
    isValid,
    errors: validate.errors,
  };
};

I want to validate 'data' object and in case of validation error I want to print error + value of severityType ('error' or'warning' or can be any value). I know it is not standard JSON validation schema, but I added it as custom filed to fetch its value to be able to act depend on severityType value in case of error of validation. How to be able to get severityType value?