Unfortunately I cannot. Shall we postpone to next week?
'Rinviamo' = rin-VIA-mo. 'Purtroppo' = pur-TROP-po.
Use this when you cannot keep a plan and want to reschedule without cancelling the friendship. Starting with 'purtroppo' (unfortunately) signals genuine regret. Immediately offering an alternative time shows you want to maintain the plan.
'Rinviare' (to postpone/defer) — 'rinviamo' is the first-person plural suggestion for postponement. 'Alla settimana prossima' (to next week) — 'alla' = 'a + la'. 'Purtroppo' (unfortunately) is a key Italian word for expressing regret about constraints.
Mi dispiace, ho un imprevisto.
I am sorry, I have an unexpected commitment.
'Imprevisto' (unforeseen event) — common Italian explanation for cancelling
Possiamo spostare a venerdì?
Can we move it to Friday?
Offering a specific alternative day
Ti confermo appena posso la nuova data.
I will confirm the new date with you as soon as I can.
Promising follow-through on rescheduling
Cancelling plans in Italy is done with more ceremony than in some northern European cultures. Simply not showing up or cancelling with a brief text message is considered rude ('scortese'). The Italian expectation is a phone call, a sincere apology, and an immediate rescheduling offer. Showing the cancellation causes you genuine regret is important.