Error while upgrading from 3.3.4 to 4.0

[vesper8]

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

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…