Failed to invalidate session

[zlehnherr1]

What happened?

Trying to sync 2 piholes, (1 primary, 1 replica). I am using TrueNAS to hold the docker containter, with the below env variables. I am doing a "Custom App" as TrueNAS calls it. Some things are changed to avoid sharing IP address or passwords.

I did allow webserver.api.app_sudo from the GUI.

Expected Behaviour

nebula sync would login and start syncing the sessions.

Nebula-sync Version

0.11.1

Runtime

docker

Operating System

TrueNAS Scale 25.04.2.6/Debian 12

CPU Architecture

x86_64

Configuration

PRIMARY = https://#.#.#.3/admin/login|[Generated APP Password]
REPLICAS = https://#.#.#.4/admin/login|[Generated APP Password]0
FULL_SYNC = true
RUN_GRAVITY = true
CRON = * * * * *
CLIENT_SKIP_TLS_VERIFICATION = true
CLIENT_RETRY_DELAY_SECONDS = 20 - added from other issues/reddit articles I have seen

Relevant log output

2026-03-10 23:59:28.516404+00:00�[90m2026-03-10T18:59:28-05:00�[0m �[32mINF�[0m �[1mStarting nebula-sync v0.11.1�[0m
2026-03-10 23:59:28.516444+00:00�[90m2026-03-10T18:59:28-05:00�[0m �[32mINF�[0m �[1mRunning sync�[0m �[36mmode=�[0mfull �[36mreplicas=�[0m1
2026-03-10 23:59:28.516465+00:00�[90m2026-03-10T18:59:28-05:00�[0m �[32mINF�[0m �[1mAuthenticating clients...�[0m
2026-03-10 23:59:28.655858+00:00�[90m2026-03-10T18:59:28-05:00�[0m �[32mINF�[0m �[1mInvalidating sessions...�[0m
2026-03-10 23:59:28.655876+00:00�[90m2026-03-10T18:59:28-05:00�[0m �[33mWRN�[0m �[1mFailed to invalidate session for target: https://#.#.#.3/admin/login�[0m
2026-03-11 00:00:08.675539+00:00�[90m2026-03-10T19:00:08-05:00�[0m �[31mFTL�[0m �[1mSync failed�[0m �[36merror=�[0m�[31m�[1m"authenticate: https://#.#.#.3/admin/login/api/auth: invalid character '<' looking for beginning of value"�[0m�[0m
2026-03-11 00:00:08.675610+00:00�[90m2026-03-10T19:00:08-05:00�[0m �[33mWRN�[0m �[1mFailed to invalidate session for target: https://#.#.#.4/admin/login�[0m

Pi-hole Version

Core [v6.4] FTL [v6.5] Web interface [v6.4.1]

[Keridos]

Having the same issue here trying to sync to two replicas. Using HTTPS to access both the primary and the replicas.

Update:
Testing using http:// to sync 1 replica works fine. I however need HTTPS to fully sync my pihole instances.

[lazydave-droid]

I was fighting this endlessly for a bit. In the end I found it didn't seem to be handling the API keys very well.
In the end:
Removing the keys, recreating and enabling, updating the config all helped.
I also spawn it from a stack in Portainer (yeah, yeah.. I know...). I had the url/api under environment:.
I changed them to variables and added them under environment variables instead - I was wondering if the use a pipe between the host and the API key might be problematic given some of the special characters I seeing in the keys.

On the off chance that saves anyone some grief....