I have fixed my problem and I am now able to detect BLE beacons and their locations.
It seems that Meraki access points don't detect beacons which send unknown data frames.
(I used beacons of ELA Innovation, which are preconfigured to send a manufacturer specific data frame. With this configuration my access points couldn't detect the beacon as they were not shown on the dashboard in the list of the Bluetooth clients)
To resolve the problem, I had to reconfigure the BLE beacons (via NFC) and change the data format.
Once I changed the format to iBeacon on all of my Beacons, they instantly showed up on the dashboard and I was able to receive their location data through Scanning API.