Combinations can only be sold online if there is one program option available per program group. For example, if you're trying to sell a combination for a movie (which is a scheduled program) in one program group and one of many options, such as different movies, in the other program group, Altru will not allow this combination to be put on sale online.

In order to resolve this, you'll need to choose only one program per program group within the combination.
  1.  Go to Tickets > Combinations.
  2. Click your combination.
  3. On the Programs tab, click Edit next to the program group that has multiple programs listed.
  4. Remove all programs but one by clicking the row, then hitting the Delete key on your keyboard.
  5. Click Save.