Why am I not getting any supply?

[UnderUsedTier]

I am inexperienced to HOI4 and I want to know why I'm not getting any supply, my units are just dying

 

[GrandVezir]

Your screenshot suggests that the supply system is trying to bring supply through the port of Split, instead of overland through Trieste. Observe the purple line leading back toward Italy from Novi Sad: it turns south to the port.

The reason it's doing so, appears to be that the rail links from Trieste to Ljubljana and Rijeka are not upgraded as wide as the line Rijeka-Split. Observe how the rails on the map are narrower from Trieste than from the coast, running into Yugoslavia.

Final piece of the puzzle: the tooltip for the supply hub in Belgrade reads: "No Convoys Have Access! Supply Fulfilment Halted!" Since your menu shows you have 255 convoys available, it seems likely that one or more of the sea zones between the port of origin and Split, has been blocked. (Whether by you in the naval interface or by your enemies' fleets is not clear from this view.)

To fix, either upgrade the rail from Trieste, or clear the sea route to Split.

 

[Deadreckoning]

Seems silly that supply doesn’t max out all available sea and rail connections.

 

[jpd]

The better question would be : why doesn't it reroute over land (even if that delivers less supplies) when the sea route is blocked.

 

[Joshua Happytree]

The better question would be : why doesn't it reroute over land (even if that delivers less supplies) when the sea route is blocked.

I'd guess railroad conversion has not been completed. Zagreb, Rijeka and Ljublana are also out of supply though they have a clear link via Trieste. @UnderUsedTier how many days ago have you taken over Western provinces of YUG?