I seem to have found out what the problem was - we are using KV Engine v2 and this plugin was designed for KV Engine v1.
I tried with application.properties:
spring.application.name=vaultdemo
spring.cloud.vault.kv.enabled=true
spring.cloud.vault.authentication=TOKEN
spring.cloud.vault.token=
spring.cloud.vault.scheme=http
spring.cloud.vault.host=127.0.0.1
spring.cloud.vault.port=8200
spring.config.import: vault://
but failed as
spring.config.import: vault://
highlights last symbol "/" in red. I learned that it is a bug but found no solution.
Does anyone know a solution to get secrets for KV Engine v2 ?