500 Internal server error - when requesting notify change for for second time

Description

When subscribing with webhook for changes for second time with the same subscriber the response status code is 500 Internal server error.

Steps to reproduce

Send the same request as in the example below twice.

curl --location 'https://vault.vereign.com/tsa/policy/policy/policies/example/locked/1.0/notifychange' \
--header 'Content-Type: application/json' \
--data '{
  "subscriber": "bace",
  "webhook_url": "https://webhook.site/4d79f1a0-9608-4d5b-9187-dfe18ae3467b"
}'

Expected

409 Conflict

Actual

500 Internal server error