Training Setup - power source: smart trainer or power-meter?

I paired a Stages SB20 trainer and 2 Stages power meters to the TR app. The power readings were definitely out by at least 50% possibly over 100%. TR help told me to unpair the power meters. I now have a trainer with 2 power meters not paired to anything. How does the TR app measure the power?My FTP is less than half it should be. I’m thinking of quitting my subscription.