Initially Audit Trail Cloud will not appear in the NXT Marketplace Activation page, in order to add it to your NXT you will need to use the app id. 


App id is: e2cf3109-f81e-4904-b90e-dc2135d95982


Login to NXT and got to Control panel, select 'Applications'



Click on the 'connect app' button


Enter the ID number and click continue