This is from the FAB technical requirements documentation:
4.2.1 Project File Link
4.2.1.a Project Versions must have a Project File Link that navigates to a hosting site (such as GoogleDrive/Dropbox/OneDrive/etc.) at which the product’s files can be downloaded by Epic.
4.2.1.b Project File Links must host the download of a zip archive, containing only one Unreal Engine project or plugin folder, for as long as it takes Epic to generate a build for those distributable files. The hosted project or plugin must be built in the same engine version as the earliest Supported Engine Version of that Project Version.
4.2.1.c If the files hosted at the Project File Link have any kind of password or encryption key that Epic needs, it can be typed into the Version Notes of that Project Version.
https://support.fab.com/s/article/FAB-TECHNICAL-REQUIREMENTS
It sounds like you only have to host the files until Epic can ingest them into their storage