Experienced Android Dev Help Needed Asap

Good evening everyone,

We have an android app ready but facing an issue making background service with notification. it's working fine below Oreo devices as per what we have working currently with our backend API. Over the above oreo devices, it keeps showing default notifications which we do not want to show. If any experienced Android developer knows how we can implement it properly in background service that would be appreciated.

Before bid please look over the requirements and we need it to be done asap, its small job for experienced with android. also, write about the best apps you've to build in your descriptions otherwise it would be not considered.

Thank you - Hiring within an Hour or something.