which routine checks the authorization in ME21N

My user was set with M_BEST_BSART. However, even though it prompt to User no authorization for the selected PO document type, it allow User to continue the entry.

The end result was a PO created but the User cannot delete it because it had no authorization for hprithe document type.

I had tried to find the routine that checks the authorization of the po document type but i still cannot find it.

Can someone me to identify the routine that checked it?

Thanks

Bye