Panasonic NN-GT576 - clock set procedure not working?

Panasonic microwave model NN-GT576.
When I try to set the time, the final step is to press the Clock Pad. When I do this, the screen says there is an error and asks me to try set the time again. So, effectively, the microwave is not working. What is wrong and how do I fix it?
Phil, July 2021
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