Consultant CTO is required for the selection of Client portal + billing platform

Hello Experts, We are looking for Client portal cum billing platform which can cater our following needs : 1) Should be able to list of contents with an attached file which can be views by the client. 2) Billing to be done on credit balance keeping ,eg 100 $ can be kept in the account and they can view the above list based on the balance available ,they can view 4 such lines if the 1 line of content will cost $25. [Either can auto hide and view or upload from our end. ] 3) Client portal login where they can view list of contents with their balance along with payment option to top up. 4) Dollar billing from across the world primarily from the USA. 5) CSV Upload option for the list of contents. What we expect from the consultant : 1) Help us to choose the right software /service which cater these needs. 2)Help us to integrate with that platform. 3) Please note that this will not need any new development ,rather the support is to select the right tool which help us cater the above needs. 4) Platform to be easy to use and less costly. We don't have any further document on this but we can provide you a MS Teams /Zoom explanation. thanks, CSI