I am trying to import a background image to my camera, but the image sequence won't load.
It says “error opening file”.
If it's not a sequence, loading one image seems to work but I need the whole sequence.

Weird but maybe its struggling with the naming, rename your file sto test.0000000.tif or sth

Your sequence starts at frame 87997. You'll need to offset that frame number by that amount minus your scene's start frame.

This can be done using an expression: