Sales Order PUT request not working with SO type WO

Regarding Acumatica API

I am developing an app with Sales Order update functionality, I’m appending customer order number with P.O number provided in ecommerce site upon order.

The problem is every time I try to update the Sales Order it is not updating. 

Upon searching for documentation and reference, I read a comment on one forum that PUT request will not work if Order type is not SO. With this I just want to verify if this is correct or if it is, is there a way to update it?

Thank you!