xml_rpc-32700 error with Jetpack and Multisite

I’m running a WP Multisite with 2 sites on it.

The first site has Jetpack set up just fine. I am trying to enable it on the second site. However, every time I try to enable it, it tells me

Your Jetpack has a glitch. We’re sorry for the inconvenience. Please try again later, if the issue continues please contact support with this message: xml_rpc-32700
Try connecting again.
Error Details: The Jetpack server could not communicate with your site’s XML-RPC URL. Please check to make sure http://mysite.com/xmlrpc.php is working properly. It should show ‘XML‑RPC server accepts POST requests only.’ on a line by itself when viewed in a browser and should not have any blank links or extra output anywhere.

When I visit http://mysite.com/xmlrpc.php it tells me:

XML-RPC server accepts POST requests only.

which is what it should say… I haven’t found any searches in the forums that relate to my issue, particularly since it works with one of the sites on the multisite and not the other. Any ideas?