The directory vqmod is not allowed to be written to!
With OpenCart 3.0 there is a new filter in the extension installer. If your module uses custom directory names it most likely will fail during install.
Install this fix to make the installer allow any directories.
How to install?
1 - Go to extension installer.
2 - Upload the installer_allow_all_directories.ocmod.zip
3 - Go to Extensions / Modifications and click REFRESH
This Step 3 is very important!!!
You should be ready by now.
Hope I saved you the hours I needed for this.
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Note for advanced users:
I took care of the installer rewriting rules and they still work.
So if you install something in catalog/controller/... and the DIR_CATALOG says that catalog is renamed to catalog123 then your module will still work and contents of upload/catalog/controller/... will go to catalog123/controller as intended in the installer.
I found this rule to be useful so I left it.
I got a lot of comments of people who claim that they still have the problem after installing this fix.
For all of you who may still experience problems after installing this PLEASE repeat Install Step 3
one more time.