Office Jet 8720 There is a problem with the supply system. Have replaced Magenta Cartridge twice.

[Master18123]

New cartridges installed twice. Error message says ,"There is a problem with the delivery system."

Magenta cartridge only. 

[Echo_Lake]

@Master18123
Thank you for posting on the HP Support Community.

I have a few troubleshooting steps we could try to fix the issue:  

Let's perform a hard reset:

1. Turn the printer on, if it is not already on.

2. Wait until the printer is idle and silent before you continue.

3. With the printer turned on, disconnect the power cord from the rear of the printer.

4. Unplug the power cord from the wall outlet.

5. Wait at least 60 seconds.

6. Plug the power cord back into the wall outlet.

   NOTE: HP recommends connecting the printer power cord directly to the wall outlet.

7. Reconnect the power cord to the rear of the printer.

8. Turn on the printer, if it does not automatically turn on.

9. Wait until the printer is idle and silent before you proceed.

Next step update the printer firmware from here and restart the printer and check. 

And, also you can refer to this document Black or Color Ink Not Printing: https://support.hp.com/in-en/product/hp-officejet-pro-8720-all-in-one-printer-series/7902032/documen...

Hope this helps! Keep me posted for further assistance.
Please click “Accept as Solution” if you feel my post solved your issue, it will help others find the solution.