Since the encrypt/decrypt endpoints on the config server are disabled (we're using client side decryption), the easiest way is to use the Spring CLI to encrypt config values.
Install the Spring CLI. You can also use SdkMan formerly GVM to install. Important, make sure you use the older 1.3.6.RELEASE of Spring CLI, otherwise you'll run into this issue.
Install the Spring Cloud CLI:
$ spring install org.springframework.cloud:spring-cloud-cli:1.2.0.BUILD-SNAPSHOT