In most cases, the cause of the error is either insufficient fees or an attempt to send a transaction that results in an insufficient CDP collateral ratio. Please try with checking them first.
If 1 does not solve your problem, please try to use one of the other node of the following nodes. (The b node tends to be unstable due to the concentration of access.)
If 1 and 2 does not solve your problem, please provide the following information to help us solve the problem.
Your address
Which transaction caused the problem? (ex. cdp create, deposit collateral, withdraw collateral, issue cdp, clear cdp, return coins to faucet or all etc.)
Your screenshot of the error
(If you can, Information displayed in the Console and Network of the browser's developer tools)
I keep getting these error codes 400 and occasionally 500