Sentence examples for then was from inspiring English sources

"then was" is correct and usable in written English.
It is often used to emphasize a sequence of events or to indicate a specific point in time. Here is an example: "John finished his work and then was finally able to relax for the rest of the evening." In this sentence, "then was" is used to show the sequence of events - first John finished his work, and then he was able to relax.