Purchase cycle control

for each of the stages in the purchasing system provided below, identify what could go wrong and what controls the system designer could implement to try and deal with these problems.
Stage:
goods received

Administration:
goods received note is issued in put to four copies to accounts, ordered, warehouse and purchasing department

What could go wrong:
goods received note not allocated to supplier account.

Control measures:
GRN to be processed as soon as received and matched to purchase orders to be investigated.
Check condition of the goods received.
regular purchase ledger reconciliation.

stage:
goods paid or returned

Administration:
payment processed or credit note received

What could go wrong:
incorrect payment made(in error or fraudulently)
payment or return not allocated to supplier account.

Control measures:
match payment amount to original invoice
regular purchase ledger reconciliations
ensure that payment is correctly authorised.

questions:
In good received stage good received note not allocate to supplier account
what items should supplier account include? why GRN not allocated to supplier account is a mistake?

In goods paid or returned stage, payment or return not allocated to supplier account is mistake,
what is supplier account? where it is from? why payment and return should allocate to supplier account?