to upload any plugin to the system, login to your server account go to file manager core -> Modules folder

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upload plugin file here, let's assume you have uploaded PaddlePaymentGateway plugin into the Modules folder. now we will enable it for the website

goto core folder open modules_statuses.json file

add PaddlePaymentGateway into the modules_statuses.json file

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that is all for upload and enable plugins for your website..