i need a file sharing app

Hey! Just wanted to share the details with you of how I want my my app. but I will prefer a flutter. I am a graphic designer. To share the files with my clients, I use Dropbox. I just want a similar app here basically : 1) my client sign in 2) download the files I work on for them. Instead of sending them the files with a Dropbox or Google Drive link, i just need them to download my app, sign in into their account and their files are there . Let me know if its clear. Looking for a simple app low cost . Let me know if it's possible. I already designed the screens and can share them with you . Thanks in advance.