The station is at the new bus terminal in front of the S-Bahn station Leverkusen-Mitte.
FlixBus will depart from the bus platforms in the east of the terminal.
International Bus Station is at Meerssenerweg behind the train station. Cross the station to reach the stop. Monday-Friday the station is opened 0545-2300, Saturday 0600-2300, Sunday 0700-2300. Outside these hours, walk around the station. Navigation can be found here:
https://bit.ly/maastrichtflix