Fix Shopify Store with Paywhirl Plugin

We have a Shopify store which integrates Paywhirl to create subscription models for my products. We had very specific requirements with the subscription which required custom javascript code, which was done by the previous dev, but he left the project halfway and did not complete it.

We are having issues managing Paywhirl on the backend, we cannot see the Paywhirl widget show up.

We are looking for an expert in Shopify and writing custom code, and someone who can help us fix Paywhirl so we can go live.