foreach error

I’m getting “Warning: Invalid argument supplied for foreach() in class-emma-api.php on line 103” and my groups aren’t showing up. Maybe as a result, any address I put in the form is generating a “Member Not Added, Member may have already been added. Please Try Again.” notification. Does json_decode depend on a server setting that I don’t have correct? Thanks in advance!

https://ww.wp.xz.cn/plugins/emma-emarketing-plugin/