There exist two different solutions to using OPC-UA with GOAL:
GOAL OPC-UA Nano/Micro Stack developed by port tailored for resource-constrained devices
A wrapper for the Open Source https://www.open62541.org/ stack for Linux .
The most recent version of the Reference Manuals for each solution can be downloaded from these links:
GOAL OPC-UA Micro/Nano:
GOAL OPC UA Wrapper for open62541:
Older Versions
2.23.0
GOAL OPC-UA Micro/Nano:
GOAL OPC UA Wrapper for open62541: