Using FTP client, copy the folders admin, catalog and system to the root of your website.

If you need to replacement file, you need to agree.

Go to the admin panel of your website. Go to menu "Modules/Extension -> Modules/Extensions".

From the list, select the extension type "Payment".

Module PayKassa should appear in the list of payment systems.

Click on the install payment module PayKassa.

After installation, click on "Edit".

You went into the settings of the payment module PayKassa. Fill in all required fields:

Status: enabled;

Shop ID: the ID of your store in the system PayKassa (can be found in the personal Cabinet);

Secret key: the secret key of your store, you can also see in the personal Cabinet;

Specify the status of orders payment

1. The status of any pending payment (default Pending);
2. The status of successful payment (default, Complete);
3. The status of the failed payment (default, Failed);

Save the changes.

Then, enter the URL address in the "Account PayKassa → Shopping → Settings → Technical"

URL successful payment

https:// *****/?route=extension/payment/paykassa/success

URL failed payment

https:// *****/?route=extension/payment/paykassa/fail

URL handler

https:// *****/?route=extension/payment/paykassa/status

Where the * * * * * is your domain

To apply the changes.
Module PayKassa for CMS Opencart 2.3.x configured.