Greetings all,
I am looking into using `org-invoice` to generate some invoices. It uses
the CLOCKSUM property, which according to the docs gets auto-generated when
the clock entries are summed in a subtree.

Concretely, docs say: "CLOCKSUM: The sum of CLOCK intervals in the
subtree.  ‘org-clock-sum’ must be run first to compute the values in the
current buffer."  However, `org-clock-sum` is a non-interactive function,
and evaluating it by hand doesn't do anything for me.

Org-clock-report is able to generate the table with total subtree sums, but
doesn't set the CLOCKSUM property.

Question: how do I get CLOCKSUM property generated and stored in a subtree
with timestamps so that org-invoice functions can pick it up?
--Leo