🇮🇳India @Prabhat Burnwal

You need to add services.yml in all your subsites. And enable the CORS for all the sites.

Add these line in services.yml file

cors.config:
  enabled: true
  # Specify allowed headers, like 'x-allowed-header'.
  allowedHeaders: ['*']
  # Specify allowed request methods, specify ['*'] to allow all possible ones.
  allowedMethods: ['*']
  # Configure requests allowed from specific origins. Do not include trailing
  # slashes with URLs.
  allowedOrigins: ['*']
  # Sets the Access-Control-Expose-Headers header.
  exposedHeaders: false
  # Sets the Access-Control-Max-Age header.
  maxAge: false
  # Sets the Access-Control-Allow-Credentials header.
  supportsCredentials: false

Make sure you add the path of your services.yml in settings.php of your all subsites.