Canon EOS REBEL T8i Advanced User's Manual page 583

Note
Certain images may not be able to be sent with [Send range], [Send all card], or
[Send all found].
When you reduce the image size, all images to be sent at the same time are
resized. Note that movies or size still photos are not reduced.
[Reduced] is enabled only for still photos shot with cameras of the same model as
this camera. Still photos shot with other models are sent without resizing.
A record of sent images can be checked when you access image.canon.
When you use a battery to power the camera, make sure it is fully charged.
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