When I was trying to do what you're doing I googled that problem.. it's a common issue with iphones, not accepting video formats other than the iphone format (not a fault of Pulsar). I pretty much gave up on trying and just use the computer now. I use the VLC computer program and convert the videos to .mp4, From there you can either facebook message it, or upload to youtube and send the video link.
For my old computer VLC crashes a lot so all I can really do is convert the file with VLC (vs edit, cut, splice, add pics, text, etc). For editing I use ShotCut.. Here's a video of the double I got on Tuesday..