Odd System.Format Exception [duplicate]

Answer 1

You need to escape the { with {{ and the } with }} because String.Format will search for an argument like {0:000} but instead finds {"dateBooking ... } which is no valid argument format. Thats why a FormatException raises.

return String.Format("[{{\"dateBooking\":\"{0}\",\"lta\":\"{1}\"}}]", dateStr, lta);