The current ecobee developer page says it is not accepting new developer registrations. A new project should not assume it can obtain a fresh API key merely by following an older tutorial.
Use the ecobee Thermostat discussion to distinguish access questions from failures in an already authorized integration. The registration restriction does not, on its own, establish that every existing integration has stopped working.
For an existing setup, begin with a read-only check of the intended device. Avoid changing schedules or temperatures simply to prove that a connection exists.
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