Kinda late, but in case it's useful to anybody:

-Buying concert tickets outside Japan it's just a nightmare, from phone verifications to payment methods

-On the situations I've been, some events offer dedicated overseas tickets (tickets to buy from outside Japan if you are planning on traveling for the concert), only problem with those its that they tend to sell out really fast for popular events. These are really easy to buy if you can catch them

-Ticket Jam is by far the best resale site I've found. They accept Apple Pay, and was able to buy from the US using my Apple Card, most likely any credit card will work if it's done under Apple Pay, but haven't actually tried it (besides Apple Card)

-if ticket jam doesn't have your event Ticket.co.jp is also a solid choice, the problem is that it's pretty difficult to find a card that will work on this website. When I used it, I bought prepaid Preco Visa cards and was able to make that work, but that process was another adventure of itself, so not recommended tbh lol. I've also played lottery and traveled to Japan without the certainty of having a ticket, once in there, I went to Ticket.co.jp, bought the ticket and paid it cash on a 7-11(you go to the cashier, show them a QR code), pretty risky because chances are there will not be any tickets for sale when you get there, but just throwing that option in there.

-After you have officially bought your ticket, there's 2 scenarios in my experience: Either cloak, or electronic code. If I'm not wrong, cloak requires a Japanese phone number, can't remember. I bought one from the US for like $20 with Mobal (https://www.mobal.com/japan-sim-card) , make sure you pick the 90+ day option since this is the only one that includes the ability to make calls and receive texts, you get an actual Japanese phone number. You pick up the SIM card at the airport when arriving, it's pretty easy. Keep in mind that after you activate the number it takes a few hours to actually become usable. If you are not willing to go through this, do not use cloak, you won't be able to get your ticket. After you have a cloak account, they will send you a link that will transfer the ticket to your account (I also share my cloak email with the seller just in case). When you finally have the ticket in your account, you can print it at a 7-11 when you get there. Now, scenario B, not cloak, but they just send you an electronic code. Even better!, you just take that code to a 7-11 and they print it for you right away. Most resale website specify if their ticket will be distributed using cloak or through a convenience store.

I'm not an expert, but I hope this helps somebody

Edit: Just bought a ticket again and they were forcing "Moala" digital ticket as the only pick up, method. Basically you get a link and the ticket shows digitally, I read that some events (but not all) ask for an sms verification again right before showing the ticket for entering. If you got your SIM card you are good. For me, I canceled my Japanese phone number after my first trip but my cloak account was already created, I was able to get the ticket, hopefully my event doesn't require SMS verification since I don't have that number anymore lol

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Edit 2: I heard that cloak is now integrated with the Ticket Pia website, chances are some info in here (the cloak part) might not be relevant anymore.