Switching from convert.exe to magick.exe

[koolsoftware]

In version ImageMagick-6.9.1-Q8 (for example), the following commands worked fine:
convert -layers Optimize *.png animate.gif (leaving out a few arguments for simplicity)
convert -layers OptimizePlus *.png animate.gif

In version ImageMagick-7.0.8-Q8, the following commands don't work:
magick -layers Optimize *.png animate.gif
magick -layers OptimizePlus *.png animate.gif
magick -layers optimize *.png animate.gif
magick -layers optimize-plus *.png animate.gif

What are the correct commands when using magick?

[snibgo]

For a long time (some years) users have been encouraged to write commands with options in the order they are to be executed. For example: read images, process them, write them.

V7 imposes some logical order. If you tell it to process images before you have read any, IM will raise an error.

For more about porting from v6 to v7, see http://www.imagemagick.org/script/porting.php