How do you find keys of a Blessed Hash?

perl-diddler has asked for the wisdom of the Perl Monks concerning the following question:

I must never have tried this before, I tried using keys on a hash I'd just blessed, only to be told that keys can't be used on a blessed object:

Type of argument to keys on reference must be unblessed hashref or arr
+ayref at ...
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How do I print the keys? I feel like I'm missing some obvious step?