unfortunately you can't force anyone to use western union, there's people that even use cashapp only despite paypal being more reliable/a huge platform, so it might not even be that they don't trust western union. it's frustrating i know but there's nothing you can do about this, buyers want convenience. they don't want to make an account and set up money transfers for a 15$ commission when they can just use their paypal to send 15$ to someone else immediately. there's a lot of good art for them to buy so it's easy for them to just use an artist that accepts paypal instead. it's part of marketing, if your product isn't accessable it's hard to sell. my solution for you is to find any way possible to get access to paypal, maybe through a friend you trust that has paypal so they can use their paypal to transfer money to you via western union.