I assume you have created a track with the ‘level’ parameter assigned, and created a curve sequence on the track. This track must be placed as a child track under the track you want to automate. Automation will search upwards in the track hierarchy until finding a track that can use the automation data. Note that if your track with the audio file has no plugins assigned, then you need to select the ‘enable audio’ option in the track properties, to make the track a mix point. Otherwise the level automation will continue further up the hierarchy.
If this does not make any sense, you could email me your project file, and I can then tell you where the problem is.
Frits