On your HomeRunner booking page, a per-guest add-on such as breakfast only lets guests select a quantity of 1.
Why this happens. When an additional fee is set up in Guesty with the multiplier Per guest or Per guest per night, Guesty calculates the fee from the guest count and the number of nights automatically. Selecting the add-on once covers every traveller for every night, and the price line in the cost breakdown shows the full amount (guests x nights x unit price). The quantity counter stays at 1 by design, because raising it would charge the fee twice.
What you can do. To make this clearer to your guests, rename the fee in Guesty to something descriptive, such as ‘Breakfast (per person, per night)’. The updated name appears on your booking page after the next sync.