i built one of those before. ftp management with user accounts. its not really a big problem to solve these days.
here's some ftp scripts you can use that have user management:
https://codecanyon.net/item/ftp-cloud/11478303
https://codecanyon.net/item/veno-fil...-files/6114247
https://codecanyon.net/item/filebear...aring/20583563
then you just need a server. if you can set up a server, rent this:
https://www.hetzner.com/dedicated-rootserver/sx62
if not, you probably have to overpay out the ass with mojo..
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