Sentence examples for was not serious from inspiring English sources

The phrase "was not serious" is correct and usable in written English.
It can be used in a variety of situations to convey that something was not intended or taken seriously. Example 1: She said she was going to dye her hair purple, but I could tell she was not serious. Example 2: I thought the breakup was just a joke, but it turns out he was not serious. Example 3: During our meeting, the CEO mentioned the possibility of downsizing, but I hope he was not serious. Example 4: The comedian's joke about politics was not serious, but it still made the audience think. Example 5: I was just kidding when I said I wanted to quit my job, I hope you know I was not serious about it.