Help with an media error

[IntroSelfie]

The php web script, with ffmpeg, that I'm using, uploads and plays videos successfully.

I have tried to add some overlay code to add a watermark to the video and am seeing this over the player on the web page:

Media error: Format(s) not supported or sources not found

mejs.download-file: https://.....com/upload/videos/6SWCpSImGQrsVXGgIh7A_24_549d36bccb10faf72b81e303ce50_video_360p_converted.mp4

any ideas/suggestions or solutions to remedy this error will be appreciated.