Supplies will only be sent to your troops and expeditionary forces under your command. If you have no troops in the East, supplies will not be sent there and they will slowly be recovered from those areas. If you have conquered land in the east and occupy it with troops, they will need to be supplied. If there is a land border, the supply AI will supply them via land, resulting in enormous loss due to the number of provinces that need to be passed through (this is realistic). If you are in this situation, it is better to force a sea supply convoy to supply your Eastern forces.
If you have forces in another (allied) country, they will be supplied by that country and the supply tip will describe these supplies as convoyed out or traded (I think that is the term it uses) but these supply transfers are "off the map". They are done to keep the hidden supply ledger balanced but they don't use convoys and (I think) they do not suffer supply transfer tax.
It's not clear exactly what is causing your problem. If you describe (or provide pictures that show) the supply tool tip, the location of your forces in the East, the ownership of land in the East and the supply routes (with the tool tip showing where supply is coming from), the community could provide better advice.