Hi Laura,
If you are in country, you can go in person to the office of the local municipality to pay your taxes. They have a department that appraises your property and determines what you owe. The tax rate is 0.25% of the appraised value of the property – this usually lower than the purchase price. You can also call your local municipality to get this information. You’ll have to speak Spanish or find someone who does.
If you have a bank account in Costa Rica, you can also pay your taxes online. Unfortunately, municipalities aren’t really set up to take online payments directly.
So if you’re out of the country and relying on your developer to pay the property taxes I would recommend you find out what your tax payment is from the municipality so you know you’re paying the right amount.