This is the script I use in Mudlet to activate MSDP.

msdp.lua

-- Enable MSDP protocol
function enableMSDP()
  -- Wait a second then try to enable MSDP
  tempTimer(1, function() sendMSDP("LIST", "COMMANDS", "LISTS", "REPORTABLE_VARIABLES") end)
  
  -- Wait 2 seconds then try to populate MSDP variables.
  tempTimer(2, function() enableMSDPvariables() end)
  cecho("<orange>MSDP ENABLED!<reset>")
end

function enableMSDPvariables()

  -- If MSDP is ready, get variables reported,
  -- else wait 1 second and try again.
  if type(msdp.REPORTABLE_VARIABLES) == "table" then
    for _,v in pairs(msdp.REPORTABLE_VARIABLES) do
      sendMSDP("REPORT", v)
    end
    cecho("<orange> -- MSDP reporting enabled!")
  else
    tempTimer(1, function() enableMSDPvariables() end)
  end
end

if event_enableMSDP then killAnonymousEventHandler(event_enableMSDP) end
event_enableMSDP = registerAnonymousEventHandler("sysConnectionEvent", enableMSDP)

And this is the event to populate HMS stuff from MSDP

m = m or {}

function msdpHandler(event, ...)
    if event == "msdp.HEALTH" then
        m.hpCur = tonumber(msdp.HEALTH)
        m.hpMax = tonumber(msdp.HEALTH_MAX)
        m.hpPct = (m.hpCur / m.hpMax) * 100
    elseif event == "msdp.MANA" then
        m.mnCur = tonumber(msdp.MANA)
        m.mnMax = tonumber(msdp.MANA_MAX)
        m.mnPct = (m.mnCur / m.mnMax) * 100
    elseif event == "msdp.STAMINA" then
        m.stCur = tonumber(msdp.STAMINA)
        m.stMax = tonumber(msdp.STAMINA_MAX)
        m.stPct = (m.stCur / m.stMax) * 100
    elseif event == "msdp.OPPONENT_HEALTH" then
        m.opHp = tonumber(msdp.OPPONENT_HEALTH)
    elseif event == "msdp.OPPONENT_NUMBER" then
        m.opNo = tonumber(msdp.OPPONENT_NUMBER)
    end
end

registerAnonymousEventHandler("msdp.HEALTH", "msdpHandler")
registerAnonymousEventHandler("msdp.MANA", "msdpHandler")
registerAnonymousEventHandler("msdp.STAMINA", "msdpHandler")
registerAnonymousEventHandler("msdp.OPPONENT_HEALTH", "msdpHandler")
registerAnonymousEventHandler("msdp.OPPONENT_NUMBER", "msdpHandler")