Ability for buyers to mark Shopping Carts in SRM as u2018completeu2019

Hi

i would like to implement additional validations when a buyer attempts to click the u201CAction Completeu201D button on a requirement in the SRM Sourcing Cockpit.

To accomplish this, the intention is to provide a pop-up box in the SRM Sourcing Cockpit with the following 3 fields based on the scenario in question

- Field 1: Existing PO number (in case a requirement needs to be applied to an existing PO)

- Field 2: Existing PO line number

- Field 3: GOA Number

can any one tel me the procedure to provide this functionality.

please let me know which BADI can work for my req.