Ok. Well, in V1.7 a more detailed downlink was added, and also made it more representative of real world transfer speeds. If it's a very long flight plan, and you're on satellite comms, it could well take 10+ minutes. You can check via the Study menus if data transfer is happening. You'd have to wait 30 minutes (as in the real plane) for a downlink "timeout". A rejected flight plan should happen when it's downlinked, and will also display in the log. You might just have to be more patient.
However, next time, please also send the FMS file, and the full flight plan route, from SimBrief so we can test it. Thanks.