It seems that Velocity added a kill switch that causes clients to be kicked when using this plugin, they do no longer want to support chat manipulation at the proxy level.
So when sending a message with the plugin will result into this:

There is a issue opened at velocity talking about this exact issue: PaperMC/Velocity#804
It seems that Velocity added a kill switch that causes clients to be kicked when using this plugin, they do no longer want to support chat manipulation at the proxy level.
So when sending a message with the plugin will result into this:

There is a issue opened at velocity talking about this exact issue: PaperMC/Velocity#804