Can I add a booking I arranged outside the system, like a visa or a private car, into my travel agency software?

Yes, nearly all travel agency software lets you record a booking you arranged outside the system. It is usually called a manual or offline booking, and it exists for the things no API sells, such as a visa, a private car, a local guide, or a hotel you booked directly with the owner.

You enter the same details you would see on an automatic booking. The traveller name, the travel dates, the supplier you used, what the service is, what it cost you and what you are charging, and any note your staff should see. Most systems also let you attach the supplier voucher, so the whole trip sits in one place. Once it is saved it behaves like any other booking, so your invoices, your customer file and your sales reports include it.

The honest limit is that a manual booking has no live connection to the supplier. Nothing confirms it for you, nothing cancels automatically, and if the supplier changes the time or the room, your software will not know until a person updates it. It is a record of what you agreed, not a live reservation. How many fields you get, and whether you can attach files, also depends on your plan.

Open a test booking on your own system, look for the option to add a service manually, and check that it then appears on the customer invoice and in your sales report. If it does not, ask your account contact whether manual bookings are switched on for you.