Please read my next comments:
1.- I reviewed this xml and I found a tag missing to avoid the 
error you need to add the tag </Root> at the end to 
close properly the xml,(see xml below). 
2.- There are diferent ways to use the xmls, commonly using Postman as 
communication channel for testing transactions, but the question here is: 
What use you need to accomplish?.
For tracking events? For shipment updates?. 
3.- Other thing I noticed is that you xml says version 20C currently we 
are in the release 21C.

<Root xmlns:dbxml="http://xmlns.oracle.com/apps/otm/DBXML" Version="20C">
<dbxml:TRANSACTION_SET>
<MX_SHIPMENTS DESCRIPTION="XXX XXX XXX" 
ORDER_RELEASE_GID="XXX.XXX" 
LOCATION_GID="XXX.XXX" 
STOP_NUM="X" 
ACTIVITY="X" 
SHIPMENT_GID="XXX.XXX"/>
</db1xml:TRANSACTION_SET>
</Root>

I hope this can helps you if not, please contact me at [email protected] for more information without cost.