Do I need my own IATA licence to sell flight tickets through your flight booking API?

No, you do not always need your own IATA licence to start selling flight tickets through a flight booking API, but it does depend on how you want to work and on the market you sell in.

Many travel agencies sell flights without holding an accreditation of their own. In that case the ticket is issued under the accreditation of the supplier or consolidator sitting behind the API, and your agency remains the seller to the customer. Your branding, your service fee and your customer relationship stay with you, while the actual ticketing happens on someone else's stock. The trade off is that the fares, the airlines available and the earnings you make on each sale are shaped by that supplier, so you have less room to deal directly with airlines yourself.

If you do hold your own licence, or you already have your own airline contracts, those can usually be connected instead, so tickets are issued under your own accreditation and you keep what you have negotiated. Whether that is possible in your case depends on which airlines and systems you are approved for, and on what your plan covers, so it is not something anyone can promise before looking at your paperwork.

There are also local rules in some countries about who may sell air tickets and what registrations a travel business must hold, and those apply to you whichever API you use. A good next step is to tell us which countries you sell in and whether you already hold any accreditation or supplier contracts, so we can tell you plainly which setup will suit you.