Ext is for External. Where you can hang a spool if you have no AMS or a filament incompatible with an AMS.
What type AMS do you have? Older type or AMS HT or AMS 2 Pro?
I have P1S so pardon if I ask a question about something P1P does not have.
On your control pad, do you see the AMS? At a minimum you should be able to see the AMS on the firmware screen. Printer will be top of the list then the AMS then buffer.
Check your cables between printer, buffer, AMS.
