Hi there @bye_ology!
This method is all about regrouping samples into categories relevant to your study - control vs treatment, before/after intervention, etc. What that error is saying is that none of your metadata values were able to create groups with more than sample in it.
Yikes, that is super low, but isn't the issue here (also, you could rarefy at 63, which would keep the same samples, but would buy you a little more depth...).
Can you provide a sample of your metadata file? Thanks! 
:qiime2: