Fix:

Discount button was greyed out due to wrong check.
  Show was sending customer as empty dictionary which triggered an error in input as id was a required column

bookie/src/app/sales/home/sales-home.component.ts

@@ -69,7 +69,7 @@ export class SalesHomeComponent implements OnInit {
   }
 
   discountAllowed(): boolean {
-    return this.auth.user.perms.indexOf('discount') === -1;
+    return this.auth.user.perms.indexOf('discount') !== -1;
   }
 
   showDiscount(): Observable<boolean | { id: string, name: string, discount: number }[]> {