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From Elxis Official Documentation

IOS Reservations has many payment modules which you can enable and set up individually for each hotel in order for for your customers to pay online their reservations surety fee. One of these payment methods, the PayPal Pro, allows you to process credit cards directly from your site and without the customer leaving the site. The PayPal Pro payment method uses PayPal's DoDirectPayment API (part of the Website Payments Pro). Supported credit cards are: Visa, Mastercard, American Express and Discover.

If you plan to use Paypal Pro on your web site make sure you have installed an SSL certificate and turn ON the SSL switch on IOS Reservations. The secure certificate will encrypt the connection and the customer will feel much safer when he/she enters his/her credit card data. IOS Reservations will automatically detect if a secure connection is available and will display the user a relative icon/message. IOS booking system will refuse access to users trying to access a secure page using an insecure connection (if SSL switch is enabled).