Note: Please remember that PayPal has its own restrictions for accounts from different countries. Sometimes you need to have a business account (e.g., Russia), sometimes a personal one is enough (e.g., USA).
To access the payments settings, click the blue Sellvia button on the top of the side panel to switch to Sellvia menu; the words on the button will change into Main menu.
Then go to Settings → Payments:
Creating PayPal App to get 'Client ID' and 'Secret Key'
Go to Sellvia → Settings → Payments → PayPal. When PayPal is not connected to your site, you'll see a notification as on the screenshot below.
Activate the Enable PayPal payment option toggle and select Rest API from the Integration method dropdown menu:
Log in to the PayPal developer account at https://developer.paypal.com using your usual PayPal login credentials.
Click that link: https://www.paypal.com/commercesetup/APICredentials
Copy your Live API credentials and paste them into your WP admin area. Click the Save Changes button.
Disable 'demo mode' when you are ready to accept payments in Live mode.
Smart Payment Buttons
Activating the Enable Smart Payment Buttons option will allow your clients to pay with their credit cards even if they don't have a PayPal account.
Hide checkout fields
The Hide checkout fields option allows your customers to skip ordinary checkout and pay with their PayPal account / Debit or Credit Card in just one click (works only when Smart Payment Buttons are enabled in your WordPress admin area).
But remember that other payment methods except PayPal will be unavailable if the Hide checkout fields option is enabled. This option is strongly recommended if you have PayPal as your only single payment gateway.
If you have any questions regarding PayPal sandbox settings, account restrictions, or settings, please contact PayPal support.
Done! For any further questions, please contact our Support Team: firstname.lastname@example.org.
If you have any issues with your PayPal account, please contact PayPal Support.