API to update PAY_ON_RECEIPT_SUMMARY_CODE := 'RECEIPT' & PAY_ON_CODE := 'RECEIPT'

I am using following API to update PAY_ON_RECEIPT_SUMMARY_CODE := 'RECEIPT' & PAY_ON_CODE := 'RECEIPT'1. When I am running the code and it ends up with following error.PAY_ON_CODE and PURCHASING_SITE_FLAG do not matchPay on Receipt Code is invalid2. For some supplier's site i have to make it null when I  update PAY_ON_RECEIPT_SUMMARY_CODE := 'RECEIPT' & PAY_ON_CODE := 'RECEIPT' then pl/sql code completing successfully but not updated any valuePlease help me to fixThe Code used:==========DECLAREl_vendor_site_rec ap_vendor_pub_pkg.r_vendor_site_rec_type;l_return_status