If you are using wordpress Mobile Domain plugin, you need to create subdomain first.
Login to your cpanel
Read this section carefully
Type your subdomain, that will be your mobile subdomain, then point the document root into the “public_html”, public_html is your wordpress installation folder, if you point it to “public_html/m” or “public_html/mobile”, the plugin will not work.
Or if your wordpress address is in the directory “blog”, such as “www.niahidayati.net/blog” then the document root should be like this “public_html/blog” and not like this “public_html/blog/m” or this “public_html/blog/mobile”
After you have created a subdomain, login to your wordpress blog. Activate the Mobile Domain plugin then go to the Mobile Domain page setting.
Type your mobile subdomain name, select the theme, click save changes.