Please check the Meeting Room Product record and ensure that the following fields have been configured:
Capacity - meaning the number of people that the room can accommodate.
Reservations Product Group - When selecting the Product Group for your Meeting Room record, please make sure that it is marked as a Reservations group. Learn more about Managing Product Groups.
Portal Availability - Please go to Additional Options, at the bottom of the page, and make sure that "Can book on Portal" is ticked.
Style / Layout - Select the style of the room so that the Portal can display it, because there is an option through which your clients can select the layout.
Start Dates - if you meeting room has a start date after the date you are trying to book, then it will not display in the search results
Learn more about Setting up Meeting Room Products.
Your Portal Meeting Room Settings (Settings > General > Portal > Meeting Rooms) allow you to hide the room layout selection dropdown on the booking page.
If you choose to do so, please set the Room Style / Layout to Boardroom. This is mandatory, otherwise the room will not be displayed onto the Portal, even if another layout is selected.