I hosted a domain on ipage. The domain is loading e.g. www.example.com but the subdomain (www.app.example.com) is not. It will just happened like that for like 13 minutes and the subdomain e.g. www.app.example.com will later be going. The major difference about the domain code and subdomain is that I check for session variables in the subdomain. If the there are no session variables , I redirect to www.app.example.com/login. The domain examples.com is a public domain whereas the subdomain app.example.com is private for certain individuals. Please, help me know where domain will be going and subdomain will not go, when the two are hosted on same account on cpanel. This is a php website using oop
I don’t know what ISP you are using, but my stupid ISP says in order to use a subdomain I have to pay extra for it. 
The only subdomain they give me for free is my original domain. Maybe that is the problem?
Thank you very much. Although I don’t totally understand how internet service provider ISP applied to this. I use IPAGE hosting service.
My ISP is IONOS and I am just guessing? It could be something else? 
Hello,
Can you access app.example.com with a simple HTML index page? That would show the sub-domain is working or not working to start with.
If you have an intermittent problem with the code routing to the sub-domain not working and later working, try contacting ipage support to see if they know what’s happening. I mean, if it sometimes works, perhaps it’s not a code problem.
How about posting your code so that you get more help from even more experienced people.
Your routing. Then the route is to sub-directory rather than the sub-domain. If it’s not going to break things, it might be worth trying.
When someone logs in, they go to https://example.com/app not https://app.example.com.
I just found this ipage support page for you: Domain Management: How to Update Subdomains | iPage