Invoice rejection error in CIG

Hi Team,

When supplier creating invoiuce he needs to input mandatory field Invoice ID# , if he gives in lower case and in S4hana invoice gets rejected , status update request in CIG its picking Upper case Invoice ID # due to which we are getting error "Bad Request" and Error Code:"400" and Error Code Response:"Error:Can not find document with documentID INVDECEMBER" .

Example :

step 1: Supplier inputs InvoiceID# "invdecemeber" in supplier portal

step2 : after invoice gets rejected in s4hana in CIG XML we can see invoice ID# INVDECEMBER ( i.e Invoice ID# is upper case in CIG Cxml file ) and Ariba comparing same ID in AN buyer due to upper case Ariba not able to find document ID in Ariba buyer account and throwing error in CIG " Error:Can not find document with documentID INVDECEMBER" "

Successful : if in step 1 supplier inputs Invoice ID # in uppercase rejected status getting replicated without error example " INVREJECT"

Could you please let us know how can we limit this and fix this issue .