Hi,
If you want to restrict the posting in MIRO, you may remove the authorization for MIRO from all users except accounts people. For others, you may give authorization for MIR7 transaction.
You may check the thread : Re: Restricting the post option in MIRO
You may check the the authorization object :F_BKPF_BUK (Activity 01 allows invoice posting)
Regards,
AKPT