[duckerude]

Running `sudo units_cur` does the trick for me.

  $ units
  Currency exchange rates from FloatRates (USD base) on 2020-05-12
  $ sudo units_cur
  $ units
  Currency exchange rates from FloatRates (USD base) on 2020-07-09

(GNU units, packed by Debian)

[throwaway8941]

In case anyone else needs this:

  # systemctl edit units-currency-update.service
  
  [Unit]
  Description=Update units(1) currency rates
  
  [Service]
  Type=oneshot
  Nice=19
  ExecStart=/usr/bin/units_cur
  
  # systemctl edit units-currency-update.timer
  
  [Unit]
  Description=Update units(1) currency rates
  
  [Timer]
  OnCalendar=daily
  AccuracySec=3h
  Persistent=true
  
  [Install]
  WantedBy=timers.target
  
  # systemctl daemon-reload
  # systemctl enable units-currency-update.timer