Undefined array key “frontend” Issue

Got error ‘PHP message: PHP Warning: Undefined array key “frontend” in /home/977869.cloudwaysapps.com/syqfgmwgpb/public_html/vendor/magento/framework/App/Cache/Frontend/Pool.php

Screenshot:

Solution:

    'cache' => [
        'frontend' => [
            'default' => [
                'id_prefix' => '91c_'
            ],
            'page_cache' => [
                'id_prefix' => '91c_'
            ]
        ],
        'allow_parallel_generation' => false
    ],