Urgently require fixes to the payment gateway API on my wordpress website. Thanks

Hi, I have a wordpress website which has a payment gateway called mangopay which has been partially integrated but previous developer was not able to complete it. The payments do not seem to be going through. My website is an online marketplace and I would like users to be able to depsit funds into their ewallets and also withdraw funds into thier ewallets. Currently the payments do not go through. The API is meant to process payments from visa/mastercard below £50 and by default any payments over £50 or made by Maestro card go through the 3D secure protocol which shifts liability and redirects to the card issuers own security page to complete the transaction. Further details can be seen here: [login to view URL] Once payments have gone through, I would like for a confirmation message to appear and the users balance on the website to be updated instantly. Also when withdrawals are made from the users account, the site does not refresh automatically so the withdrawal feature can be used again. Could this also be fixed. And finally if a user tries to withdraw funds without having input their bank account info a screen pops up and prompts them to enter their bank account info. Currently if the user inputs their bank account info the fields are pre-populated with irrelevant data. Can these not appear there. Also when a user inputs thier actual details, it allows them to proceed to make a withdrawal but when they click on the button again the 'banking info' screen re-appears unless you click refresh. Can this refresh automatically once the user inputs thier details and makes thier first withdrawal so they do not need to refresh manually. Another issue is that there if a user needs to update or change thier bank details, there is a button they can press which brings up the screen which allows them to enter thier new details, can this screen be pre-populated with the details the user entered last? Also, when a user creates a wallet they need to input some details into a form generated by the API. Can the fields for date of birth, nationality be changed so that the user has to select the values from drop down menus? And could the field for 'country of residence always be 'GB' by default and not changeable as my website currently only is functional for GB residents. Finally I would also like for, when a new seller registers an account and tries to bid on a job without having created an ewallet I would like for them to be prompted to do so before being allowed to proceed and bid for a job on the site. I was hoping that this process/flow could run smoothly and then be changed to the live/production environment. This needs to be done for both the Buyer and seller user accounts and also the WP-admin user account which is the same as the buyer account. Please message me to clarify any details and please NO placeholder bids. Thank you Jas