# T406

> duplicate handler

**Severity** Error

There are two handlers for the same subscription and event, for example two `on chart.close` blocks. Each subscription/event pair has at most one handler, so the execution order is never in doubt.

Merge both bodies into one handler.

## Failing example

```flowscope
script "Close and delta"
data chart = subscribe(data.ohlcv)
plot c = plot.line(title: "Close")
pane p = pane(title: "Delta", height: 0.2)
plot delta = plot.columns(title: "Delta", on: p)
on chart.close {
  c.plot(chart.close)
}
on chart.close {
  delta.plot(chart.buyVolume - chart.sellVolume)
}
```

## Fixed example

```flowscope
script "Close and delta"
data chart = subscribe(data.ohlcv)
plot c = plot.line(title: "Close")
pane p = pane(title: "Delta", height: 0.2)
plot delta = plot.columns(title: "Delta", on: p)
on chart.close {
  c.plot(chart.close)
  delta.plot(chart.buyVolume - chart.sellVolume)
}
```

## Related

- [T405](/docs/scripting/reference/diagnostics/t405)