UPM fails to upgrade plugins with Unexpected token message on console

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Platform Notice: Server and Data Center Only. This article only applies to Atlassian products on the server and data center platforms.


Sometimes UPM fails to upgrade plugins and a popup error message appears. It says it failed and to check the Confluence logs but the logs have no errors.


Confluence 7.x


Open the browser’s console and try to upgrade a plugin. You will observe the following message:

Failed to parse response text: SyntaxError: Unexpected token U in JSON at position 0


The "Unexpected token U in JSON at position 0" is a typically Javascript error that will show up in your console log if the client has been directed to execute JSON.parse() on a string beginning with u instead of a stringified object. "u" is typically a stringified version of the undefined primitive.


  1. Clear the browser's cache or use the incognito mode
  2. Try to upgrade the plugins again

Last modified on Jun 24, 2022

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