LED flashes but no transmit

I'm using Intelliremote to transmit an IR code using the UirtTransmit AutoIt script function.
When running the function the LED on USB-UIRT flashes but the receiving device sees nothing. (tried several devices with same response).
I'm using UirtTransmit("434D014405F5"), which is a learned code from the device remote.
Where should I look/what to test next?
TIA.
When running the function the LED on USB-UIRT flashes but the receiving device sees nothing. (tried several devices with same response).
I'm using UirtTransmit("434D014405F5"), which is a learned code from the device remote.
Where should I look/what to test next?
TIA.