7.1.5. Macro assignment fails

1. Is a cable connected to the parameter? Remove it. A parameter has one driver at a time.
2. Is the parameter already on a Macro? Remove it from that Macro first.
3. Are all eight slots used? Delete a Macro you no longer need.
4. Can that parameter take a Macro? On/off toggles, whole-number controls and mode settings that change a node's structure cannot. See Macros and DAW automation.

Still stuck: check Compatibility and known limitations, then contact support with your DAW version and plugin format.