It is not possible to edit/delete an allowance that has been approved (status=4).
It is only possible to change allowances that are in status 2 or status 3.
This is due to calculations performed in the background when approving the allowance. 

If an allowance has been approved by mistake/other and must be corrected or deleted, the HR manager must create an adjustment line correcting the value. 

Then a new allowance line can manually be created with the correct value.