Trying to reinstall OS X but every time I enter my Apple ID and password it says “try again later”

Which Mac model and year are you on, and do you absolutely need El Capitan here? I ask this because El Capitan is comparatively difficult to get to.

If your Mac runs newer versions of macOS, that’d generally be a better choice, and (much) easier to get to.

Do you know the Mac model and year?

And can you tell us what happened here that you’re now contemplating re-installing macOS? Why I ask? A number or folks asking for this sequence have had corruptions, somebody then suggested a re-install, and—if these corruptions are due to a failing hard disk drive, for instance—a re-install won’t fix that.

If you really need El Capitan and can’t run something newer, here’s the general sequence involved: OS upgrade - Apple Community. You will need another Mac, and particularly one capable of running El Capitan. (There’s another way that doesn’t, but it’s… even more complicated than this path.)

If your Mac and your apps can run High Sierra or newer, that’s the path to take: How to get old versions of macOS - Apple Support

Whatever you pick, have backups of your data.

Thanks very much for the detailed reply. The machine in question is a MacBook Pro 13 in. mid 2009 (5.5) Model A1278, with 8 GB Ram and an aftermarket 500 GB HDD. I've replaced the battery once. My understanding is that OS 10.11 is the most recent that it can run. The person I want to give it to has no Mac, and plans to use it to test the compatibility of a website they're working on with Safari, including older versions. I will try the path you suggest under "How to get old versions of macOS - Apple ". Thanks again!

El Capitan has a multi-step process to build an installer, and that path requires a second Mac and particularly a second Mac capable of running El Capitan. That’s discussed both in the Apple article, and in the other link.

OS X 10.11 is at the edge of being able to make a secure network connection these days, too.

That MacBook Pro 13” mid 2009 model is limited to OS X 10.11, yes.