Ketores on Klaf
What is the heter to write the parshas haketores on klaf in ashuris? I am aware that the Kaf Hachaim and others bring down the practice and that it is a segula for parnasa, but why is it okay to write it in the first place? I am vaguely aware that there is a shayla about whether or not it is muttar, but I'm not aware of who discusses it explicitly. Any sources would be appreciated.