Best answer by djraveinpeace
Thanks for visiting the help forums :)
Now, Im not an FL user myself, Reason is my D.A.W of choice, but Im pretty confident that the .flp file is the project file, ie all the sequencing data etc for your tune, its not an actual audio file.
Soundcloud support the following audio file formats: AIFF, WAVE (WAV), FLAC, ALAC, OGG, MP2, MP3, AAC, AMR, and WMA files. WAV & MP3 are probably the most commonly used. You will need to export your tune from FL as an audio file which should be pretty straight forward.
Here is a, hopefully, useful youtube video that will give you a step by step instruction on how to export (or render as this youtuber terms it) your FL song to an audio file. It seems you have a few options of how your file is exported but WAV or MP3 are your best bets (I personally would go for WAV for mastering purposes but MP3 will give you a smaller audio file size if you just want to upload straight away).
I hope this helps.