Cannot find version 9.6.18 for postgres

[SunnyGhj]

Cannot find version 9.6.18 for postgres (Service: AmazonRDS; Status Code: 400; Error Code: InvalidParameterCombination; Request ID: 50f4bee7-0dda-44
a6-8425-72e2d198e817; Proxy: null)

[SunnyGhj]

Airflow_db creation error and change to another version, such as 10.1, 12.2, this error still exists