Hello FTers. A few questions from a recent trip that I hope you can help with!

I booked a CW LHR-LAX using a TA and a GUF2. The TA was able to add the infant to the booking but not issue the ticket, they told me I would have to pay 10% of the adult fare at the ticket desk when we check in. I called BA and they said that the TA should be able to issue the ticket but because it's a TA booking nobody at BA could touch it. Both the TA and BA were slightly vague about pricing but said it should be 10% of what I paid for each seat.

You can probably guess where this is going but when I got the the ticket desk expecting to pay ~£100 (10% of the ~£1,000) but was presented with a bill of ~£1,000 (10% of the full fare).

I'd like to know what others have experienced trying to do this. Is adding an infant usually problematic? How much should the infant ticket have cost? Is there a better TA I should be using!

Thanks!