If you haven't resolved this issue yet, you may want to contact DirectAdmin support for help. The module POSTs a suspension via the API command CMD_API_SELECT_USERS, with a location set to CMD_SELECT_USERS. Normally, this would suspend the user in DirectAdmin and respond back to Blesta that there was no error performing this action, however, the DirectAdmin API returned an invalid HTML response that is not expected for that end point, which leads me to believe that the DirectAdmin API or or its configuration has gone awry.