EBS - Search String for Electronic Bank statement

I am trying to subsitute the Posting Rule if the String' Check' is found on the note To payee.. I am litte confused as to how to do this.

External transaction is say 100, posting rule currently is AB03 , if it finds the text 'Check' it should replace Posting Rule to AB01.

External transaction 100 is mapped to AB03.

External Tranasaction 200 is mapped to AB01

I am on ECC 6.0 and on the 'Search String Defination' i have given ' Check' as the search string. What do i need to give in Mapping ?

in the Search String Use , I have given the Company code and the Target as Posting Rule also algorithm as NO interpretation.

However it is not working.. When i try to upload a bank statement it does not change the posting rule.

Can you please tell me what i am missing here.

Thank you.

M