# Issues querying MCP server

**URL:** https://forum.mattermost.com/t/issues-querying-mcp-server/25827
**Category:** Agents & AI
**Created:** [April 1, 2026, 3:01pm UTC](https://forum.mattermost.com/t/issues-querying-mcp-server/25827 "2026-04-01T15:01:53Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![ata-mpa](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.mattermost.com/ata-mpa/32/9411_2.png) [@ata-mpa](https://forum.mattermost.com/u/ata-mpa)
#### Post date: [April 1, 2026, 3:01pm UTC](https://forum.mattermost.com/t/issues-querying-mcp-server/25827/1 "2026-04-01T15:01:54Z")

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I’ve enabled the MCP server via the agent plugin, and my LLM can see and detect the list of tools, but whenever it tries to interact with it i get the error below.

`Error: invalid session token: failed to decode JSON payload into AppError. Body: Client sent an HTTP request to an HTTPS server. : invalid character 'C' looking for beginning of value`

This is a self hosted instance running with TLS with LetsEncrypt certs on the normal 443 port.  
Server Version: 11.3.0  
Database Schema Version: 148  
Build Number: 20708891798  
Database: postgres

Has anyone else ran into this issue?

Many Thanks,  
Matt