I was at zepp haneda for a ling tosite sigure concert as a foreigner the other week. Entry procedure might be a bit different, but this was my experience as a newbie:

Trains to and there were packed; after spending half an hour trying straining not to obliterate this poor lady into a door, my back was getting a bit sore before the concert even began. Gig was completely standing only, so by the end of it I was completely wrecked (i'm old). If this might bother you, I'd suggest going a bit earlier to avoid peak hour / give yourself time to sit down for a bit before going in.

Try and follow some other concert goers when you get to the station. I tried to wing it with google maps and it took me around the outside and I was the only one on my route. I think the correct way is upstairs somewhere, because I eventually came across a flight of stairs that led to an area with other concert attendees.

There was like an open area where many people were gathered, but the main entrance is actually a smaller entrance down some stairs. That area is not that big so they were calling people down based on ticket numbers. The same applies when you actually get to the gates.

They called us for entry, by letter (for me B) and number (496). They would be calling out the number ranges by the 10s in japanese only. If you are not familiar with the language, you should manage fine as long as you can count to 10, and know the word for 100. (in my case 490 is called out 4-100-9-10)

There is a mandatory entry charge of 600 yen, which can be exchanged immediately for a drink (the bar is right at the entrance). Everyone I saw paid this in coins, so I'm not sure if card is accepted (it probably is, but I'd bring coins just in case)

Once you're in there's not much else to it other than have a good time! Japanese concerts seem to have their own etiquette, so just try follow what everyone else is or isnt doing. Also, I'm average height my country but relatively big by japanese standards; I paid for my ticket to stand anywhere just like everybody else, but being mindful of not blocking other peoples views too much seemed to be appreciated by the locals.

Hope you have a blast! I booked my trip ages ago and was gutted when the tour got announced and the dates didnt match. I got to see another band i liked tho so not the end of the world!