OneDrive and DropBox on iPhone will not sync if they are closed

My OneDrive and DropBox will not sync photos on my iPhone unless they are opened. I have checked both apps settings and they are allowed to run in the background. Also, both are allowed to use cellular data. So, basically, I followed all the recommendations however it seems they only sync when they are opened. iCloud syncs fine and I can see all my photos in the cloud. Any idea or tips on how to make OneDrive and DropBox work in the background?