Sometimes we need to dynamically set URL for migrations, for example we have specific parameters restricting results.

We have default configuration

source:
  plugin: url
  data_fetcher_plugin: http
  data_parser_plugin: json
  urls:
    - 'http://your_domain/data.php'

// Get configuration factory.
$config_factory = \Drupal::configFactory();
// Load your migration configuration.
// Replace with your migration ID.
$migration_config = $config_factory->getEditable('migrate_plus.migration.[MIGRATION_ID]');
// Set your URL here.
$migration_config ->set('source.urls', ['YOUR_URL']);
$migration_config ->save();