How can I further troubleshoot this and get to the bottom of it? Ideally resolve it...
You really can't.
The transaction you sent is confirmed.
The recipient address is
3DTjFxbN1k8sFi5ro65sdYKSh1QauThzYw.
If this is the address he gave you, you did your part. The coins were sent
and received. For everything else, your "friend" is responsible.
Blockchain transactions are irreversible.
Your friend gave you the wrong address? There is nothing
he can do.
What you are saying is the same as
-"Transfer me some money. My account number is 123456"
-"Ok, done"
-"Oh sorry, my account number is actually 654321"
Whose fault is that? Who should try to troubleshoot?
But, as I said, there is still a possibility: Your friend is using a shitful wallet which is not syncing. He may still receive his funds.
Is he using a wallet or an exchange?? This is an important question I think.
As for you, I would just tell your friend this:
Your money is where you told me to send. You can check here:
https://blockstream.info/tx/4ebbddc16281d9c12cbaa7bfcf83346a45e9ab27224a3f292a44403d321cf2ec