HTTP 500 with no further details

[yaakov-h]

I'm running both ghost:6-alpine and activitypub:1.1.0 in podman and have nginx terminating both.

I have the reverse proxy configured as per ghost 6 release notes.

When I enable ActivityPub under Settings > Growth > Network I see the following in activitypub container log:

11:25:51.739 INF activitypub: 'GET' '[site]' 'https://[site]/.ghost/activitypub/v1/site' '94da8a29-3392-432f-ba9e-f34bf734cc56'
11:25:51.743 INF activitypub: KnexKvStore: Get key cachedJwks,blog.yaakov.online
11:26:07.885 INF activitypub: 'GET' '[site]' 'https://[site]/.ghost/activitypub/v1/site' '94da8a29-3392-432f-ba9e-f34bf734cc56' 500 16146ms

I see the following in ghost container log:

[2025-09-09 11:26:07] ERROR Could not get webhook secret for ActivityPub FetchError: invalid json response body at https://[site]/.ghost/activitypub/v1/site reason: Unexpected token 'e', "fetch failed" is not valid JSON

How can I go about diagnosing why this request fails after about 15 seconds?

This is reproducible by disabling the (broken) AP integration and then re-enabling it.