You connect to BitShares DEX via a Full Node provider. If the Node is laggy, or really busy at the time, it is possible that your request does not got through.
Luckily, there's an easy fix (other than running your own full node):
- Click Settings

- Click Full Node API Server
- Select a new one
- Click Confirm Button
you're reconnecting to the Blockchain now and you should be able to use it without further problems.
If Polo's down, Polo's down. If BitShares is down, just select another full node :)
Click Here to check it out!

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Steem: ash @ steem ─ Steemit How-To's

Unlike Dashs Masternodes, you can run it for free. Nice post Ash.