Simple multi-user app + backend for UK subcontractor payments

UPDATE: The application should be scalable and ready to accept a mobile app at a later stage. All functionality as described below, referencing the attached document.
Note that I will supply mock ups of all pages, graphics, and proformas for all documents. I also have extensive documentation to support all integrations, present and future.
The app should be fully functional and able to support up to around 50 users for test purposes, scalable later with ease.


What this is

I need a small, practical system for UK construction businesses to pay subcontractors correctly under the Construction Industry Scheme (CIS).

Multi-user (must-have)

Multiple companies/contractors can use the system.

Each company can have several employer users (e.g., owner + bookkeeper), each with their own login.

Subcontractors have their own login to submit applications.

Users should only see data for their own company (clean separation).

Simple user management: add/remove users, reset passwords.

What it should do (Phase 1)

Subcontractor side (web app): log in and submit an “application for payment” (labour, materials, reference).

Employer side (web app): log in, review and approve/reject/edit applications.

Automatic maths:

CIS is taken from labour only (0%, 20% or 30%).

VAT (if VAT-registered) applies to labour + materials.

Outputs we need:

Payslip PDF emailed to the subcontractor when approved.

Bank CSV (date, name, sort code, account, amount, reference) to upload for payments.

Monthly CIS summary for the tax month (6th–5th) showing labour totals and CIS deducted.

Security & access: email + password login, password reset, HTTPS.

Hosted so a small team can use it for a live pilot.

Nice to have (Phase 2 – separate later)

HMRC CIS sandbox: verify subcontractors and submit monthly returns.

Simple subscriptions (Stripe/GoCardless).

CSV tweaks for Xero/Sage.

What I’ll provide

Clear rules for CIS/VAT calculations.

A tiny prototype and example spreadsheet showing the flow.

Copy/text for emails and payslips.

What I’m looking for

Someone who can ship a tidy multi-user web app with a web backend (API + DB).

Comfortable with PDFs, clean CSV exports, basic user management, and deployment (Render/Fly/DigitalOcean).

Pragmatic UX—straightforward screens are fine.

When it’s “done” (acceptance)

Live, HTTPS site with multi-user logins.

I can: create a company → invite employer users → subcontractor signs up and submits an application → employer approves → download bank CSV → subcontractor gets payslip PDF → download CIS month summary for 6th–5th.