Discord, Slack and many forum or email-style uploads cap attachments at about 8 MB, which is why a clip that looks small still gets rejected.
Keep clips short and focused: a 30 to 45 second clip at 720p fits comfortably, while a minute of 1080p footage will need the resolution lowered automatically. The tool aims for roughly 93 to 95 percent of the limit so the finished file does not tip over it.
Need a different ceiling? Use the related pages for other common upload caps, or the general FileHost.net Video Compressor for manual quality control.