We're having the same problem with dsd. Dh tries to speak to her every day for a few minutes but she won't answer her phone. She won't come here unless we're doing something which is rare as we can't afford it. The only time dsd will answer the phone is when she asks for money.
It really upsets dh that she's like this. She's not interested in just hanging out at home or going to the park. We have fair rules that apply to all the children, and yes she shares a room here but she does at home too. We are more strict than her mum but at home she's allowed to jump on the furniture and is basically given whatever she wants as long as she's not bugging her mum. Dsd has even told us she doesn't want to come as we never go anywhere, she likes going to the pub with her mum instead.
We can't afford the pub every month never mind every week and dh is knackered after working all week so just wants to relax at the weekend. We don't have a car either so walk everywhere which dsd also doesn't like.
Tbf dsd has always been like this and dh and I used to have to take her to soft play every weekend or she'd refuse to see him, even though he's always done his best for her. She's too old for soft play now and has said that we should take her to theme parks and the like and then she'll come, that isn't going to happen.
Part of the problem is that when parents split the children can choose who to spend time with and are obviously going to choose the parent that is doing things and giving them things. Whereas when parents are together the children don't have a choice. Our dcs don't always like being at home and want to do things but they can't just say "I'm going to grandma's if you don't take me somewhere" they just have to get on with it and find fun things to do like playing out or going to the park.
There's also this attitude that it's something the nrp is doing or something wrong with the relationship that stops the child not wanting to visit unless they get treats and days out. It can never be that the child has become a spoiled brat after being bribed for so long. If it was a resident parent saying that their child was demanding days out every weekend the response would be to nip it in the bud and remove privileges, don't be manipulated not the what is her dad doing wrong, it's not her fault etc you get when you post about a step child.
Bribing and pandering to children to get them to see you us just setting you up for problems. It's bloody hard and horrible when nrps are faced with this situation but you can only ride it out and keep trying.