Currently, there is an error when trying to upload mp4s as custom videos for exercises.

There appears to be an error on the network call to get the upload URL
{code: 2000, message: "Cannot upload exercise video on a free plan.", data: null}
code
:
2000
data
:
null
message
:
"Cannot upload exercise video on a free plan."

You should inform the end user that this is an unsupported feature for the free plan instead of showing a generic "video not uploaded error" in the user interface.