Hi Jittima,
In your step 3, you must put commitment item field status as optional also, like Funds Center.
The minimum FM account assignments that I mentioned is that when PSM-FM is activated as in your system, in all screens you must have derivations for Funds Center and the same for Commitment Item. That's why you need to change Commitment Item in your step 3 to be optional at least.
In other words, to have budget you must have content for fields Funds Center and Commitment Item and of course you can use the other FM fields also as in your case that you are using Fund.
Regards, Vanessa.