fixed config definition

src/DependencyInjection/Configuration.php

@@ -28,12 +28,14 @@ final class Configuration implements ConfigurationInterface
                         ->isRequired()
                     ->end()
                     ->arrayNode('cache')
-                        ->scalarNode('ttl')
-                            ->info('TTL for cached API calls')
-                            ->example([1800, 'P30M'])
-                            ->defaultValue(1800)
-                            ->cannotBeEmpty()
-                            ->isRequired()
+                        ->children()
+                            ->scalarNode('ttl')
+                                ->info('TTL for cached API calls')
+                                ->example([1800, 'P30M'])
+                                ->defaultValue(1800)
+                                ->cannotBeEmpty()
+                                ->isRequired()
+                            ->end()
                         ->end()
                     ->end()
                 ->end();