Sunexpress Fails to Assist with Esta Visa for My Portugal Passport to US Flight

I have successfully traveled from İzmir to the US using my Portugal passport on Sunexpress three times without any issues. However, on 12/7/24, the check-in desk officer struggled with the process and was unaware of the Esta visa requirement for my travel. Additionally, they failed to coordinate with United Airlines, forcing me to check-in again in Paris.
I would appreciate if you could look into this matter and provide a resolution. As a frequent flyer with Sunexpress, I expect a higher level of service and support, especially when it comes to navigating visa requirements for international travel.