SAP APO GATP Online / In-Class Training SAP Global Available to Promise (GATP). It is part of SAP SCM-APO tool. GATP is like promising to customer demands based on some predefined availability checks on your existing stocks. It uses ATP rules to decide whether the customer demands can be confirmed against the available stocks. It is a tool by which you try to maximize your servicing capacity to the customer by using different methods of GATP. Global ATP checks the entire network (other plants), product / material substitutions defined in the condition and also production from alternative location based on the advanced functionality called Rule based ATP.