"User authentication failed due to invalid authentication values" Error

If you are receiving this error when a customer is processing payments and using Authorize.net as your payment processor, here is your solution:

1. Go to your Authorize.net account and regenerate a new Transaction Key
2. Head to My Account > Accept Payments
3. Click on "Authorize.net"
4. Copy this key into Printavo 
5. Hit Save

If you are receiving this error when creating a shipping label, here is your solution: 

Head to My Account > Shipping > Re-enter API Key