Grammar

When we use me and I

Subject function  - I eat an apple
Object function - When the pronoun is in the predicate and acts as an object, or carries a preposition in front of it.  " he helped me " o " he sat between you and me ". ( no between you and I " ).

Sentences

- He's planning TO TRAVEL to London.✔

- He's planning A TRIP to London.✔

- He's planning A TRAVEL to London.X . Is not correct.