# Error while upgrading from 3.3.4 to 4.0

**URL:** <https://forum.mautic.org/t/error-while-upgrading-from-3-3-4-to-4-0/20686>\
**Category:** Mautic 4 Install/Upgrade Support\
**Created:** [September 2, 2021, 8:53am UTC](https://forum.mautic.org/t/error-while-upgrading-from-3-3-4-to-4-0/20686 "2021-09-02T08:53:29Z")\
**Posts on this page:** 1\
**Showing post:** 5

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**Author:** ![vesper8](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.mautic.org/vesper8/32/2043_2.png) [@vesper8](https://forum.mautic.org/u/vesper8)\
**Post date:** [November 17, 2021, 12:06pm UTC](https://forum.mautic.org/t/error-while-upgrading-from-3-3-4-to-4-0/20686/5 "2021-11-17T12:06:22Z")

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This is how I was able to resolve my problem once and for all. Now I have a fully upgraded and clean installation of v4

> [@Was unable to update to 4.0, here's what finally worked for me](https://forum.mautic.org/t/was-unable-to-update-to-4-0-heres-what-finally-worked-for-me/20980):
>
> I’ve been updating Mautic since v2 and I guess I had some old problems with the DB schema. I was on 3.3.1 and I was able to update to 3.3.4 no problem, but then all hell broke loose when I tried to update to 4.0 I was getting errors related to the oauth2\_clients table foreign key constraints. I wasted a lot of time trying to figure this out, finally what worked for me I created a brand new 3.3.4 install, allowed the installation wizard to create a new database. I then dumped all of my existi…

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