Follow the instructions:
1. Download the latest version of WP Rocket
You must reply to see links
2. Extract the file with Winrar and Use NotePad++ or any tool that you use for coding to open the following files.
3. Open the WP-Rocket folder > inc/functions/options.php.
4. Replace the block starting with “function rocket_valid_key()” with “return true” exactly in the same way as you can see it in the screenshot below.
5. CTRL + S (Save it).
Make a zip file of the folder and upload it to WordPress.
Note: Every time a new version of the plugin come, you have to download the latest version and edit the file. Then upload it.