I put this in the list configuration page as

explained.

 Renewal= 6-monthly, delay (14) 

 Then I get this error message when I submit it.

 I also tried 7 as a delay value,, same result.

 Renewal- 6-monthly, delay (7)

 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  The following problems have been detected in the list header:

* Renewal= ...,DELAY
Error: Invalid parameter value. Please consult the list keyword documentation
for a description of this keyword, whose syntax is too complex to
describe here.

Please refer to the list keyword documentation (available via the "INFO
KEYWORDS" command) for more information about keyword syntax.

PUT operation rejected, old list remains unchanged.