The issue is in your blocks, not the script (at the moment)
You also have a typo in your post test:
fileanme instead of filename
See below, using KIO4_Base64 extension, the filepath for the image picked and the need to remove some of the path. Also see the encoded text to show that the image is being encoded.
You need to do this checking and debugging for each step in your workflow to ensure you have everything correct and working.