Person I purchased from can’t claim funds

Description

I bought something from someone on Depop and I received the item and everything. However my payment is pending and I keep telling the seller it’s because they haven’t accepted the payment. I don’t think they understand what to do because of course it’s on them so there’s not really much I can do, and I keep telling them to contact customer service but according to them it’s not working. They want me to cancel the payment and pay them via Venmo but I know that’s against Depop’s rules so I don’t want to do that. From their side, what steps do they need to take to accept the money? I know I shouldn’t be doing the work for them and it’s technically not my responsibility but I’m annoyed they keep on messaging as if it’s my problem.