Sometimes, one small thing can stall all your progress.
If you find yourself coming across a guard in the Let’s Go games that won’t let you enter the city unless you give him a hot beverage, then you are not alone.
To get to Saffron City originally in Pokémon Red and Blue, trainers had to get a drink from Celadon City to enter Saffron. This isn’t the same in Let’s Go, however, as you’ll need to give the guards Tea instead.
So how do you get the time, you ask? Well, in short, Tea is given to you as part of the story. You need to progress through the game long enough so that you reach Celadon City. You can then find Brock, who is West of the Pokémon Centre, after getting the City’s Gym badge.
If he still isn’t there, then you might have to clear out Team Rocket as well from the game centre.
You’ll then be able to head to Saffron City and continue to progress through the game.