Develop upsell functionality for GiveWP WordPress Plugin

We are a humanitarian aid charity. Due to the nature of our work, we have relatively little money to spend on administrative costs. We would like to increase this income through upselling donations on our website, which will allow us to function better as a charity.

The core plugin are are looking to utilise is GiveWP. It is designed for donations but it does not have the upsell feature we desire. Please familiarise yourself with the product:
Official website: https://givewp.com/
WordPress repository: https://en-gb.wordpress.org/plugins/give/
Github: https://github.com/impress-org/givewp

We have seen upsell functionality in other funnel plugins and want this integrated into GiveWP. The funnel plugins are similar to Clickfunnels which you may be familiar with:
Cartflows (https://cartflows.com/)
WooFunnels (https://buildwoofunnels.com/woocommerce-one-click-upsells-upstroke/).

I have attached 5 screenshots.
The first three screenshot are taken from GiveWP’s demo page (https://givewp.com/demos/): Step1-default.jpg, Step2-default.jpg, Step3-default.jpg, these are the default flow currently used by GiveWP.
The last 2 screenshots are mockups I have created: Step4a-custom.jpg and Step4b-custom.jpg show a initial mockup of what the upsell could look like.

This piece of development must use GiveWP’s PayPal/Square/Stripe gateway tokenization process to send a tokenization request. The gateway would return a “token.” If the donor accepts the upsell then a charge against that token is created.

Please submit proof of previous development work you have done if you are interested in taking on this work.