I've seen this question answered in a few posts but, to be honest, the solution doesn't work to me.
Everywhere it says to add the following on the textbox:
If (Checkbox1.Value = false, DisplayMode.Disabled, DisplayMode.Edit)
I've also tried to add the following on the checkbox triggers:
OnCheck : TextInput5.DisplayMode.Edit
OnUncheck: TextInput5.DisplayMode.Disabled
But look at the video, it changes the Textbox text but doesn't do anything.