Need a simple ios and android app to select contacts from phone and send them to an online database api

We need a simple app where user can select multiple contacts from phone contacts and upload these to an online database api (via rest api end point) The app should also be able to read the contacts uploaded by user - again via api which will return the data in json format. This reading of the data is to show the already exported records as ticked in the app so that user who opens the app knows which records are already uploaded and which are not. He/she cannot select a contact that already exists in the spreadsheet. Also if the phone number exists in our online database with a different name it should grey that out in the contact list in the app so that those records are also not selectable for upload. User should be able to view the online database data from the app and also edit the name column and also delete rows from the google sheets - right from the app. There should be a mechanism to identify the user of the app to the online database so that only those records belonging to the user are available to the user on the app. The online database we are using is knack and you will have to use the knack api to do the job.