Crazing. This zap is the zap of NWC of cashu that I bound through Freerse. It worked. 

Feedback two questions, 

The first zap 21sats were deducted twice 21sats. Probably because after clicking zap, I immediately went back to the cashu wallet page. 

The second problem is that I zap 2sats, and the client shows success, but the cashu wallet does not deduct success.