Error when trying to create a task without start and end date

Hi there,
I need to create tasks without a start and end date, how is it possible?
Right now, if I try to create a task without these dates I get an error.

Yes, it is possible to do that. You just need to add unscheduled: true option to them. Unscheduled tasks are displayed in the grid by default, but they are not displayed in the timeline as they usually don’t have dates.
You can read more about it in the following article:
And here is an example how it works: