Custom language model not showing for real-time transcription

In the 'Amazon Transcribe' -> 'Custom language model' section I have a model I have uploaded via s3. It has completed processing, and the language is showing as 'en-GB' for the model.

If I go to the 'Real-time transcription' section and set the specific language to 'en-GB' then go to the customizations section and toggle 'Custom language model'. The drop down shows 'No options' instead of showing the relevant CLM.

Are there any other steps I need to take to get this to show up?