Saturday afternoons break fragile till systems. The queue is long, the network is slow, and a client is standing at the counter waiting for a prompt on their phone. Payment flow matters most exactly then.
Send the request once. When you ring up a sale and trigger an STK push, the transaction is created in a pending state and the sale is not marked paid yet. If the client does not respond, or the network drops, check the sale again later instead of starting a second payment; the POS settles a pending sale when the callback confirms it.
Let the desk see what is pending. A short list of unconfirmed payments tells the receptionist whose receipt is still owed, and stops a client leaving with an unpaid bill. Marking a sale paid by hand should be an exception with a reason, not a habit.
Always hand over a receipt with a reference on it. It is the single line both you and the client can quote if a payment is questioned a week later, and it turns an awkward phone call into a lookup.
Keep your pay bill keys secure: they belong to the salon, are encrypted at rest, and only your manager-level logins should be able to change them.