couldn't obtain engine version for global cluster try calling region where the global cluster has members

The error you're encountering with write forwarding for your global cluster appears to be related to version compatibility or configuration issues.

Write forwarding is a feature that allows secondary clusters in an Aurora global database to forward write operations to the primary cluster, reducing the need to manage multiple endpoints. However, there are specific requirements for this feature to work properly.

To troubleshoot this issue, consider the following:

1. Version compatibility: Write forwarding is supported in specific Aurora versions. For Aurora PostgreSQL, it's supported in all minor versions of version 16 and higher (and specific minor versions of earlier releases). For Aurora MySQL, it's supported in version 2.08.1 and higher.

2. Engine version consistency: Global cluster operations (including enabling features like write forwarding) can be blocked when not all regional clusters in the global cluster are running the same engine version. If you see an error about obtaining engine version, this might be the case.

3. Check version status: You can verify if all your clusters are on the same version by checking the maintenance status of each cluster in your global database. If there are pending maintenance actions for any cluster, apply them to ensure all clusters are on the same version.

4. Region-specific operation: As the error suggests, you might need to make the API call from the region where the global cluster has members. Try performing the operation from the AWS region where your primary cluster is located.

To check if write forwarding is already enabled on your secondary clusters, you can use the AWS Management Console or run an AWS CLI command to check the "GlobalWriteForwardingStatus" attribute, which should show "enabled" if it's working properly.
Sources
Disaster recovery and Amazon DocumentDB global clusters - Amazon DocumentDB
Using write forwarding in an Aurora MySQL global database - Amazon Aurora
Using write forwarding in an Aurora PostgreSQL global database - Amazon Aurora
Using write forwarding in an Amazon Aurora global database - Amazon Aurora