The advertiser can send you viewing appointments for the flat directly in the messenger.
The advertiser has the possibility to send viewing appointments in the messenger. The applicant can accept or decline a viewing date proposal. Hence you have a good overview on all of your viewing appointments.
Some flats do have a lot of contact requests. Advertisers are able to pause the flat advertisment which prevents more contact requests. But if you have arranged a viewing appointment you still will be able to write messenges at any time and view the advertisment itself.