Here are some steps to try if your Amazon device is having trouble discovering the thermostat:

• Ensure that you authorized the correct Mysa account to your Amazon Alexa account, this is the same email address that you used to create your Mysa account.
• Make sure that your Mysa thermostat is on the latest firmware. If it is a new installation, give it several hours to update. After it is updated, Alexa should be able to connect to Mysa. 
• Disable and re-enable the Mysa skill in the Alexa app.
• You’ll need to make sure the thermostats are online in the Mysa app on your phone before giving a voice command to Alexa. For networking and connectivity troubleshooting, click here.
• For additional troubleshooting, click here.

If none of the above steps work, it often helps to Disable and re-enable the Mysa skill in the Alexa app.