Base44 App Development Troubleshooting

Hello. I am not certain this will work and want to talk about it first, but I am having major issues. I have already built an app through base44 called “FarmerLink” and it is live on the App Store. Apple rejected my in app purchase setup multiple times, and every time I tried to setup an “in app purchase” it messed everything up that I had built. I don’t want to mess up my app anymore, I have people using it currently and need this to be a clean transition if this is possible and would work. I would like to charge every user a monthly fee of .99 cents to use my mobile IOS Apple App on their phone, so I need an “in app purchase” feature. However, as I said before, Apple won’t accept it and it has messed up my app multiple times and I don’t want that to happen again. Lastly, I don’t want anything to change with my app or website and how it’s setup already. I also don’t have a lot of money to spend as I’ve spent so much already, so I guess I would like to know a couple things before I commit to this if possible. One being, will this work, is it possible? And is there a chance this will mess up my app/website or will it change anything? Lastly, how much would it cost to have this setup? Am I only paying you once to set this up? I do not want to pay more than once. Not sure how upwork works. I greatly appreciated the help. Look forward to hearing from you.