If you try to connect through WLAN, it is the IP given to the phone by the DHCP of the access point, or if you are trying the USB-cable, the default is 192.168.2.15
More info about this in at least these articles:
https://jolla.zendesk.com/hc/en-us/articles/202011863
https://jolla.zendesk.com/hc/en-us/articles/202004823