HTTP Error after finishing uploading a video that is bigger than 64 MB -> After raising the upload limit manually in the wp-config file

Question

I use Dreamhost as my web host. Previously my WordPress upload limit was 64 MB. I asked the tech from Dreamhost to boost it to 400MB. He told me I had to change a setting in my wp-config.php. That's what did:

Here's the code I added in:

define( 'WP_MEMORY_LIMIT', '400M' );

We also changed the setting in the phprc file to fit the max size.

When I refreshed my dashboard to upload new media files, That max limit shown was 400MB. So I was happy and went on to upload my video (123 MB). The upload seemed to work (as in it was actually starting to upload). And it reached 100%

But at 100% a nasty HTTP ERROR happened and now I don't see my video my media library (meaning that it did not upload). I can still only upload files that are less than 64 MB.