Freelance Developer Needed: EDI Integration for Purchase Order & ASN Systems

We're seeking an experienced backend developer to implement a comprehensive EDI (Electronic Data Interchange) integration system for our 10-minute delivery platform. The project involves building robust API integrations for Purchase Order creation, acknowledgment, and Advance Shipment Note (ASN) synchronization between our retail system and vendor/supplier systems.
Project Scope
The integration consists of two primary modules:

1. Purchase Order (PO) EDI Integration
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Implement webhook endpoints to push PO creation data to vendor systems in predefined formats (JSON/XML)

Build PO acknowledgment flow to receive processing status from vendor systems

Handle synchronous and asynchronous PO processing workflows

Support both immediate response and delayed acknowledgment patterns

2. Advance Shipment Note (ASN) & Invoice Integration
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Develop webhook endpoints to receive ASN and invoice data from supplier systems

Implement comprehensive validation logic for ASN header fields and item-level data

Build error handling for partial acceptance, full acceptance, and rejection scenarios

Create digital invoice verification against PO/TOT values

Support batch detail pre-feeding to warehouse systems

Technical Requirements
API Development:

RESTful API design with POST endpoints

Support for both JSON and XML payload formats

Basic Authentication implementation

HTTPS/SSL encryption

ISO-8601 UTC timestamp handling

Integration Features:

Webhook configuration and management

IP whitelisting support for security

Comprehensive error code system (E101-E114 range)

Warning notifications for non-blocking issues (W101-W103 range)

Detailed error parameter tracking with field-level validation

Data Handling:

Parse and validate complex nested objects (buyer details, supplier details, item data, tax distribution)

Handle GST calculations (CGST, SGST, IGST, CESS)

Support batch numbers, UPC codes, HSN codes

Manage unit of measurement conversions

Track shipping and e-way bill information

Deliverables
PO Creation Endpoint that accepts purchase order data with:

Complete buyer and supplier metadata

Item-level details with pricing and tax breakdowns

Contact and address information

Custom attributes support

PO Acknowledgment System that handles:

Processing, accepted, partially accepted, and rejected statuses

Error and warning arrays with contextual parameters

Asynchronous processing support

ASN Sync Endpoint that receives:

Invoice and shipment details

Tax distribution summaries

Item-level data with batch tracking

QR/barcode traceability codes

Expiry date and manufacturing date validation

Comprehensive Error Handling including:

ASN-level and item-level error differentiation

HTTP 2XX responses for partial/full acceptance

HTTP 400 responses for complete rejections

Detailed error descriptions with actionable parameters

Documentation covering:

API endpoint specifications

Authentication setup guide

Sample request/response payloads

Error code reference guide