It seems you use an old instruction. Please check the following one:
Code:
To enable Login with PayPal in your X-Cart shop:
1. Open the following URL:
https://developer.paypal.com
2. On the Developer Portal page, click Log in.
3. On the Developer Portal page, click Applications.
4. On the My REST apps page, click Create App.
5. Enter application name, click Create app.
6. Make sure the Log In with PayPal option in the APP CAPABILITIES section is enabled.
7. Click edit next to App redirect URLs and specify this location for both URLs:
http://yourstoreurl/pplogin_return.php
8. Click Advanced options next to Log In with PayPal and enable Personal Information, Address Information, Account Information, specify other options (e.g. privacy URL:
http://yourstoreurl/pages.php?alias=business) if required.
9. Copy and and paste Application Client ID and Secret options values to corresponding fields below and click Apply changes button.
That's all. Do not forget to log out of the Developer Portal.