Recently I purchased a flight from booking.com and needed to Star Alliance Frequent Flyer to the booking so I could use my gold rewards.
I raised a case with with airline “Air India”
This is in reference to your query related to booking changes, we would like to inform you that, this booking was made by the travel agency “ETRAVELIGROUP AB”
We recommend you make changes through the travel agency you made the booking, if you made the reservation by Air India we would definitely help you but in your case, the booking is made by the travel agency.
I then raised a case with Booking.com
We appreciate you for choosing booking.com for your flight reservation. We have received your request to add a frequent flyer Air Canada number to this booking. We would like to inform you that we are unable to add a frequent flyer Air Canada number to this booking. We request you, please contact the airline for further information.
I then had to follow up booking.com support saying the airline could not do this! Who finally agree they could do this
We appreciate you choosing booking.com for your flight reservation. We would like to inform you that we have well added your frequent flyer Air Canada number (XXXXXX) to this booking. If you have any other query please contact us again we will be glad to assist you.