OP wrote:
"Yes a 2014 Mac mini. The internal drive is bootable with 10.13.6. The external has not os on it at this time as I can not install it."
OK.
I'm going to give you
the best advice I can.
I suggest you try EXACTLY what I suggest.
PRINT OUT this reply and follow it EXACTLY.
Then come back and give us your report.
First, you will need CarbonCopyCloner.
Get it here:
https://bombich.com/download
You want CCC 5.
CCC is FREE to download, and it's FREE to use for 30 days.
THIS WILL COST YOU NOTHING.
Put CCC into your applications folder.
Now, connect the external SSD that you have. Use the new enclosure that you bought for it.
Open Disk Utility.
Go to the "view" menu and choose "show all devices" (you can also type "command-2").
Select the external drive.
You want to click on the "topmost" line for the drive, because this represents the physical drive itself.
We're going to NUKE IT into oblivion and start over.
Now click the erase button.
Choose "Mac OS extended with journaling enabled, GUID partition format".
Then give it a recognizable name.
Then erase it.
It will take a few seconds, then it should appear on the desktop.
The drive is "empty" and waiting for us to fill it.
OK, we're going to have to take a break here, because I forgot to ask you before.
Please answer these questions before we can go further:
1. How much space is currently used up on your internal drive? (in gb)
2. How large is the SSD that you bought? (in gb)
Again, PRINT THIS REPLY OUT for reference.
Get back with the answers and I'll tell you what to do next.
WHY I need the answers:
We don't know if the SSD can "hold everything" that is on the internal drive.
There are ways around this, but we need to know the answers before proceeding.