DemoLoop is the Apple demo app, which means you will need to discuss this with the seller.
If you bought it used from a third-party, I’d suspect this was stolen from Apple.
Assuming it’s not stolen… The seller (maybe you got this directly from Apple somehow, and Apple messed up?) will need to perform the following steps: Sell, give away, or trade in your iPhone - Apple Support
This releases the iPhone from their ownership, re-initializes it, sets up the welcome-to-i{hone “hello” setup, and transfers ownership to you. If the owner doesn’t release ownership, this iPhone won’t be particularly useful to you, and you won’t be able to get around Activation Lock.
If stolen, this won't clear ownership and won’t clear Activation Lock, and this iPhone won’t be useful. Contact the seller and request resolution or refund.
Previous reply (outdated):
Could you explain more and provide some more background about, as how you got here and which app or service or setting is involved here is unclear.
I’m unfamiliar with an app named “demo lobe”, and searches aren’t finding much matching that. (Edit: “DemoLoop”)
Is this an app you have installed, and that is not working? if so, contact the seller as was mentioned above.
If this app was already installed, was this iPhone purchased new, or from a private sale?
If this was purchased from a private sale, did you start out with the ”hello” welcome to iPhone setup? That means all apps installed are part of iOS.
If this is an iPhone with the Apple Store demo software installed, it’s quite possibly stolen.