Building a Shopify Payment App for a Payments Processor

I need an experienced developer to create a Shopify Payment App for a Payment Service Provider (PSP). The app should have robust payment processing capabilities and ensure secure transactions.

Key Requirements:
- Development of a Shopify Payment App with a primary focus on efficient payment processing.
- Strong emphasis on security to ensure safe and secure transactions.
- Experience in working with Payment Service Providers (PSPs) or similar payment systems.

The ideal freelancer for this project should have:
- Proven experience with Shopify app development, particularly in the payment processing field.
- A strong portfolio demonstrating successful payment app development.
- Prior experience working with PSPs or similar payment systems.
- Ability to deliver within a tight deadline - the project needs to be completed as soon as possible.

Please include relevant examples of your past work and experience in your proposal.