Google map is not working in Angular and giving an error of InvalidKeyMapError

Question

I just installed agm/core and related stuff to use maps using these commands

npm install @agm/core --save
npm install @types/googlemaps --save-dev

And then i imported AgmCoreModule like this in my module.ts

import { AgmCoreModule } from '@agm/core';

imports : [
    AgmCoreModule.forRoot({
      apiKey: 'my api key',
      libraries: ['places']
    })
]

And inside of my component i just used map like this

<agm-map [latitude]="latitude" [longitude]="longitude" [zoom]="zoom">
  <agm-marker [latitude]="latitude" [longitude]="longitude"></agm-marker>
</agm-map>

But i am getting this error

Google Maps JavaScript API error: InvalidKeyMapError

I don't know why this error is occurring. Can any one let me know?