Bootable media command not found

Once you downloaded the El Capitan .dmg file from Apple, did you double-click on the .dmg file to open it, then run the ".pkg" file inside it so that the El Capitan installer app is created and placed into the Applications folder?

Please make sure to carefully read the instructions in this Apple article regarding the El Capitan installer download:

How to create a bootable installer for macOS - Apple Support

Also, when posting the contents of the Terminal window, it is much better to paste the contents into the "Code Insertion" tool on the forum editing window which looks like "<>" since it is much easier to read and spaces are easier to discern which can be critical when deciphering possible typographical errors on the command line.

Hello RBJ000,

Thanks for reaching out to Apple Support Communities. Upon review of your post, it seems that you are having an issue creating a bootable installer for your Mac. We can see why you’d want this taken care of, so let us help from here! Let’s start by reviewing the following article which may help: How to create a bootable installer for macOS. Can you confirm you are following these steps?

If so, and the issue persists, further assistance may be needed. We want to make sure you reach the right team for help with your Mac, so we recommend that you contact Apple Support directly. Depending on your region, you may be able to reach them here: Get Support.

Thank you for participating in the Apple Support Communities and have a wonderful day.