Purchased basic economy ticket. Tried to check in with App to get boarding pass but was directed to check in at airport with United Staff day of flight since I'm only bringing personal bag and needed to confirm it met requirements. Arrived at MSN 1 hr before boarding and there was 15+ ppl at United counter waiting to be checked in. Used Self Check in Kiosk and was then given same message to wait for staff to check bag so I can get boarding pass. After 10-15 mins, 1 United worker finally arrived to help people with getting boarding passes and checking luggage. After 30 mins, was finally helped at counter but then denied boarding pass but wasn't given reason why and asked to wait until they checked in the now 20+ people waiting in line, missed my 6:40am flight. Waited 45mins -1.5 hr for another United staff to come out and help and reschedule to next available flight 5 hrs away. NEVER had I ever needed to check in at the airport with Staff to make sure personal bag met requirements so I can get my boarkding pass that I paid for with another Airline. Never been treated disrespectfully, unprofessionally, and dealt with incompetent Airline Staff until booking with United. Flight Return home was the same, had to check in at airport to access boarding pass. Was only able to get home on time by checking in at airport 5 hrs in advance. Instead of overbooking flights and screwing paying customers, United needs to limit flight purchases/reservations to what's available like any other Airline.