Indicate the variable to use

roles/matrix-backup-borg/tasks/validate_config.yml

@@ -11,5 +11,5 @@
 - name: Fail if encryption passphrase is undefined unless repository is unencrypted
   fail:
     msg: >-
-      You need to define a required passphrase.
+      You need to define a required passphrase using the `matrix_backup_borg_storage_encryption_passphrase` variable.
   when: "matrix_backup_borg_storage_encryption_passphrase == '' and matrix_backup_borg_encryption != 'none'"