Hi, Ron 

Currency rate of invoice header does not match currency rate of invoice posting line. 
 

@Adam.Bereda  Thank you again for your reply. 

I just want to know the parameter the date that the system to pick the conversion rate from?  

I am not sure if I know it by heart. 
Please keep in mind that curency rate application to invoice header/lines and to PO matching line are two different processes. The parameter you highlighted is applicable to invoice header/lines. 
 

@Adam.Bereda Thank you for your input.