Need to update input field label on runtime in ng-formly

Need to update input field label on runtime in ng-formly .

    {
      key: 'forename',
      type:'input',
      templateOptions: {
      label: 'Forename'}
      expressionProperties:{
        label:(model)=>//code to change label on runttime
       }
   }

expression properties not taking label. Is there any other way

To achieve this, you will need to use the expressionProperties and set the templateOptions.label to your desired label. Here is a simple example:

import { Component } from '@angular/core';
import { FormGroup } from '@angular/forms';
import { FormlyFormOptions, FormlyFieldConfig } from '@ngx-formly/core';

@Component({
  selector: 'formly-app-example',
  templateUrl: './app.component.html',
})
export class AppComponent {
  form = new FormGroup({});
  model: any = {};
  options: FormlyFormOptions = {};
  fields: FormlyFieldConfig[] = [
    {
      key: 'isApplying',
      type: 'toggle',
      templateOptions: {
        label: 'Change the label',
        description: 'Toggle Description',
        required: true,
      },
      expressionProperties: {
        'templateOptions.label':
          '`${model.userName || "User"}  is ${!model.isApplying ? "not": ""} changing the label`',
      },
    },
    {
      key: 'userName',
      type: 'input',
      templateOptions: {
        label: 'User Name',
      },
    },
  ];
}    

As per the docs, expressions allow you to dynamically change field properties. More information can be found over here.

Hope that helps