Nest Learning Thermostat Won't Display a Key After App has Disconnected

[CraigInMiami]

Have had my Nest thermostat almost 18 months.  It has worked with the Nest App on my iPhone with zero issues.  Today I had to sign in on the app.  No big deal.  But it wants me to "Add a Product".  During this procedure, each time it asks for an entry key.  I follow the instructions, go the thermostat, choose "Settings" then dial over to "Nest App" and every single time it says "Already connected to an account".  It will not under any circumstance show an entry key, which prevents me from moving forward on the app while attempting to add a product.  Please help.  

[MplsCustomer]

@CraigInMiami 

The most likely reason for what's happening to you is that you inadvertently signed back into the Google Nest app with an incorrect email address (one that had never been used for Nest, which is why it asked you to "Add a Product"), rather than the email address you were previously using to sign on. The message saying your thermostat is "already connected to an account" most likely indicates that it is connected to that previous email address, NOT to the email address you're trying to use right now.