ZXPCAU03 user exit in MIRO

Dear Experts,

I wanted to ask if somebody knows why warning message does not get displayed in transaction MIRO when using user exit ZXPCAU03. I'm checking some bank accounts and then want to issue a warning message. In transaction FB60 it works fine, but in MIRO it does not get trigerred.

Message id 'Z1' type 'W' number '801'.

Otherwise maybe you know other places where I can enter warning message on document save in MIRO.

Thanks a lot!