Why don’t you hust use a DSPATR(PC) (position cursor) on the credit card number field. I woudl use an indicator to condition the keyword and if the CHG is entered and the credit card# is blank, set on the indicator and redisplay the screen. The cursor will be positioned to the credit card number field. Make sure you set the indicator off when no error exists.
RTNCSRLOC is used to show what field the cursor was on when you press an F-key, etc. This is handy when you allow users to prompt for code values in certain fields. When they posiiton the cursor to a field and press an F-key you would have a routine that looks at the field name returned and call the appropriate prompt program.