if anyone is able to access their portal (I could access this weblink but not anymore), this document states that all fare classes can be sold either as Light, Essential or Flex fares,
and once tickets for a particular fare class have been sold out, the next higher fare class will automatically be sold, & so on

https://www.cxagents.com/content/dam...s_20230719.pdf

would be glad if anyone were able to access & download it!