UK ETA approval does not automatically guarantee entry to the UK.
A UK ETA is an electronic travel authorisation required before travelling to the UK, but final permission to enter is decided by a border officer upon arrival.
During border checks, you may be asked to confirm your passport details, purpose of visit, length of stay, and plans to return home or travel onward.
Even if your UK ETA has been approved, you may be refused entry if you do not meet the UK entry requirements.
Before travelling, you should check that your UK ETA has been approved and prepare any relevant documents that may help explain your purpose of travel and stay in the UK.