Online check-in Aerolineas MAS - https://www.check-in.site

As of my last training cut-off in September 2021, I don't have specific information regarding the online check-in process for Aerolíneas MAS, an airline based in the Dominican Republic. However, the general procedure for online check-in for most airlines includes the following steps:

1. Visit the official website of the airline.

2. Look for an option labelled "Online Check-In", "Web Check-In", or something similar, typically found in the main navigation menu or under sections like "Manage Booking" or "Travel Information".

3. Click on this option, and you'll usually need to enter your booking reference or ticket number and your last name.

4. Follow the on-screen instructions to complete the check-in process. This typically involves seat selection, and you may have the option to print your boarding pass or receive it by email or mobile.

Online check-in usually opens 24-48 hours before the scheduled flight departure time and closes a few hours before the flight.

However, this is a generalized guide, and the specifics can vary from one airline to another and may have changed since my last training data in September 2021. Always refer to the most recent information provided by the airline on their official website or contact their customer service for the most accurate and up-to-date information.