Replace World function not working or allowing to upload local save.

The replace world function doesn't allow me to replace the realms world with my local save game that I've put a lot of time into. the file size of the world I'm trying to upload is ~380MB. My PC is connected to the router via Hardwire and I have Fiber Internet so I know my speed isn't an issue. Have been trying off and on for 3 days now before making this report, I know others are having this issue but I can't find an answer anywhere else