[GNC] Newbie trouble deleting transaction

[Paul-A]

I've just started using gnucash, and have imported a few years worth of
data successfully from a bank account.  Afterwards I manually entered
two more transactions, where one is mistaken.

I'd like to remove the mistake, but am unable to do so with either
the Delete button or "Delete transaction" menu choice.  Shouldn't I
at least get some error if something is failing?

The transaction I'm removiing is blank except for a date.

Am I missing something obvious or could something be wrong with my
4.13 setup on Debian bookworm?