this will take a little hand coding in the Server validation interface, but it can be done.
Select required/ not blank for the validation type.
for the server variable, click the lightning bolt icon and select the number of appointments form element.
the code for the server variable will look like this:
change it to:
(((isset($_POST["APPTS"]) && $_POST["APPTS"] == "1"))?$_POST["apptCompany"]:"NA")
this will validate the apptCompany form element if 1 is selected in the APPTS form element, otherwise it will pass "NA" to the validation to pass the required validation.