Use incompatibility groups for manual modifiers

Hi,

I am trying to setup a manual modifier to add from the quote line. However, there is a similar modifier that currently exists.

Those two have to be available in the same timeframe but must not be both applied on the same line.

The two modifiers are setup with the same qualifiers. On the modifier line, both modifiers are in the same phase sequence, have the same precedence and the same incompatibility group.

When I apply one of them, I can still apply the other.

How to resolve this incompatibility and prevent one to be applied if the other is ?