He said he got the auto-update dialog from Messenger Plus!, but he signed out of Messenger and cancelled to dialog. Now that he signs back in to Messenger, he doesn't get the dialog anymore and he wants to update.
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dayory/nicolas,
The update window will appear again later on in a few days.
Nevertheless, if you want to update now, you can always manually download the latest version from the official website,
here and install it.
You do not need to remove the current installed version.
The setup downloaded and installed by the auto-update is always exactly the same as the one you'll find on the official website. There is no difference.
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