[SOLVED] api returned unexpected data - expected json body, got text/html

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raeserfisk

New Member
Jan 22, 2026
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Hi!

I am running Proxmox Datacenter Manager 1.0.2 (via Unraid/Docker). Its working great (love the software!) and I've managed to add 1 Proxmox Backup Server host and 3 different Proxmox hosts without any issues.

When I try to add my 4th Proxmox host I am suddenly hit with "api returned unexpected data - expected json body, got text/html" when clicking next on the "Settings" page where i've added Remote ID and login token. It doesnt matter if I try to login and create token OR if I create a token at the Proxmox host and use that one.

I've installed all 4 Proxmox hosts in an identical way so I cant see any obvious differences between them that would explain this issue.
 
Could you post what version is the affected Proxmox VE is running? Thank you!
 
Is there a proxy between the PDM instance and the Proxmox VE instance?
 
sterzy said:
Is there a proxy between the PDM instance and the Proxmox VE instance?
Click to expand...
The PDM is behind a reverse proxy but that's the case with all the already added Proxmox hosts. The infrastructural settings are 100% identical between pve1 and pdm, pve2 and pdm, pve3 and pdm.. and so on. The now failing connection is behind pve4 and pdm. 1-3 + pbs is working fine.

Update:
- I tried connecting via IP to bypass reverse proxy. No difference :/
- I tried setting PDM container to host (from bridge). No difference.
- The only version difference I find is that the working instances all run pve-manager version 9.0.11 or older. The instance NOT working is running 9.1.2 Nevermind. I just updated two hosts to identical versions (9.1.4) and this one instance still won't be added.
 
Last edited:
check your reverse proxy and PVE access logs..
 
fabian said:
check your reverse proxy and PVE access logs..
Click to expand...
PVE-log (from PVE-log):
Feb 03 10:24:29 pve pvedaemon[1025]: <root@pam> successful auth for user 'root@pam'
Feb 03 10:24:46 pve sshd-session[213443]: Connection closed by 192.168.0.181 port 55778

NPM-log (from proxy-host-XX_error.log):
2026/02/03 10:35:15 [error] 2965#2965: *88517 upstream timed out (110: Connection timed out) while reading response header from upstream, client: 192.168.0.181, server: pdm.myinternaldomain.com, request: "POST /api2/extjs/pve/scan HTTP/2.0", upstream: "https://192.168.0.171:8443/api2/extjs/pve/scan", host: "pdm.myinternaldomain.com", referrer: "https://pdm.myinternaldomain.com/"
2026/02/03 10:38:27 [error] 2965#2965: *88517 upstream timed out (110: Connection timed out) while reading response header from upstream, client: 192.168.0.181, server: pdm.myinternaldomain.com, request: "POST /api2/extjs/pve/scan HTTP/2.0", upstream: "https://192.168.0.171:8443/api2/extjs/pve/scan", host: "pdm.myinternaldomain.com", referrer: "https://pdm.myinternaldomain.com/?"

The above when using reverse proxy domain.

When trying 3 times in a row through the IP instead it finally worked. Thanks for bearing with me :)
 
raeserfisk said:
When trying 3 times in a row through the IP instead it finally worked. Thanks for bearing with me :)
Click to expand...
Alright so it was just a matter of the PVE host timing out/being to slow for your proxy and the response through your proxy returning a text error page or something like that. Is everything working as intended now? In that case please mark this thread as resolved, thanks :)
 
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sterzy said:
Alright so it was just a matter of the PVE host timing out/being to slow for your proxy and the response through your proxy returning a text error page or something like that. Is everything working as intended now? In that case please mark this thread as resolved, thanks :)
Click to expand...
I think for all intent and purpose: it is :) I'll close it for now.

Thank you kindly once again!
 
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