Enable logging
It would be nice to see what's going on.
I have a VPS that's running iodine server and works perfectly when tested from (https://code.kryo.se/iodine/check-it/)
However, AndIodine does not connect at all.
I have port 53 (TCP+UDP) open, IP forwarding enabled, and applied the iptables rules.
My device can DIG the host and resolve DNS lookups without a problem but AndIodine says "handshake failed".
Before the error dialog appears, a chunk of text, which I presume is the log, gets flashed for a split second and disappears.
Server: CentOS 7
Client: Note 8/Pie