One of the reasons why the video or audio you are sending on Facebook Messenger fails is that messenger does not meet the messenger's upload specs. The maximum attachment size is 25 MB. So you may need to change the video resolution for sending the file on messenger. The correct dimension for a video should be an aspect ratio range of 9:16 to 16:9 with a maximum frame rate of 30 frames per second. Video with more than this frame rate will be decimated in whole integers until it falls within the said range. It is resampled for audio according to the initial video sample rate to 22,050 Hz or 44,100 Hz.