Go to ecartpay.com and head to the Integrations section.
Click on Download to obtain the .ZIP file corresponding to the Prestashop module.

Log in to your PrestaShop account and, from the control panel, open the Modules > Module Manager menu.
In the top right corner, click on Upload a module.
Select the .ZIP file you downloaded and click Open to start the installation.
Once the installation is complete, the Configure button will appear. Click it to continue with the setup.
The system will ask you for a public key and a private key.
To obtain them, open a new tab and go back to ecartpay.com.
Log in to your account or register if you don't have one yet.
Within the Ecart Pay dashboard, in the left side menu, select Integrations > API.
Copy your public key and private key.
Paste both into the corresponding fields within the PrestaShop module.
Click Save to finalize the configuration.