Cannot Detach Volume

Hello all, still experimenting with freenas and have run into an issue I can not resolve and need your help.

I am trying to detach a volume to re-create it as a new volume (experimenting with different raid types). The problem I have is when I choose to detach volume in the GUI I get the error posted below.

I am not worried about the data on the drives, I just want to delete the volume.

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Request MethodOST
Request...

Cannot Detach Volume