To test if the Sparks are defective, you can test with a tech tool we have, ShineTech (available for iPhones). You can download the app from the App Store by searching ShineTech.
You can log in using this information:
How to test Sparks with ShineTech:
Step 1. Near the machine, launch the ShineTech app (make sure the machine is on)
Step 2. On ShineTech, go to the Activate tab by clicking it at the bottom
Step 3. Click on the big circle button to Scan active devices installed in the machines
Step 4. The machine ID should appear on this section and if not, it confirms that the Spark is defective.
Step 5. To test a machine, select the six-digit machine ID you wish to activate. Enter the vend price set on the machine's actual programming to start.