Arduino Uno wired to a SparkFun ATECC608A crypto co processor. Learning to use this chip for prototyping a hardware wallet-like device.

Using the SparkFun library, configured the processor successfully to default settings, including private key locked in slot 0.
Public Key successfully generates.
I am expecting a 64byte signature to generate using the private key in slot 0 (locked in the default configuration), and to be able to print that in the serial monitor.
However the createSignature() function taken from the library keeps failing.

The wiring has been triple-checked.
Configuration (example 1 from the SparkFun_ATECCX08a_Arduino_Library) done without error so assume I2C connection is adequate.
Example 2 from same library also compiles and uploads, but does not generate signature.

Debugging createSignature() has pointed to a failure in loadTempKey().

Thinking it perhaps to be a hardware issue, I used a new non-configured SparkFun ATECC608a and got the same error in createSignature() and loadTempKey().