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Download WP Rocket – Best WordPress caching plugin
Open the file /wp-rocket/inc/functions/options.php in code editor and go to line 504, replace the block starting with “function rocket_valid_key()” with “return true” exactly in the same way as below:
function rocket_valid_key() { $rocket_secret_key = get_rocket_option( 'secret_key' ); if ( ! $rocket_secret_key ) { return true; }