A few days ago a technician installed a new Nest Thermostat at my house, which was free under a program of the LADWP.
The tech asked me to download the Nest App. Which I did.
He asked me to put my home wifi into the thermostat. Which I did.
Then he asked me to open the Nest App and connect it to the Nest Thermostat.
And when I tried to, the App said, "Cookies are disabled. Please disable cookies."
The tech had to leave my home to go to his next appointment. That was about 10am.
For the next four hours I called Nest, I called Apple iPhone, I called T-Mobile.
My app would not connect to the thermostat.
Finally, about 3pm, I reached my second Nest tech on the phone.
Patiently, he directed me to go to Safari and register myself at the nest.com/login
When I registered on the Nest site it accepted me.
Then I opened my app and used the same login and password to connect to my thermostat.
TO CONNECT YOUR IPH0NE NEST APP WITH YOUR NEST THERMOSTAT YOU MUST FIRST GO TO NEST.COM/LOGIN
That solved my problem.