In late Nov 2019 you may have received a letter from the Australian Government Department of Human Services titled: "We are upgrading our digital health and aged care channels".
This is about Medicare Online changing their underlying technologies. The functionality will remain largely similar though (at least initially).
Medilink is committed to implementing these upgrades in the near future, and will announce their availability soon.
You must be using the upgraded software by March 2022.
Also as discussed in the letter, you should register for a PRODA/HPOS account if you have not already. Please go https://humanservices.gov.au/hpos to log on and check and/or register for one. Note that we (Medilink as your software vendor) don't have any control of and essentially cannot assist with this process, you must liaise with Medicare directly.