Add WhatsApp Floating Button to NodeJS App

I need a floating button integrated into my NodeJS marketplace web application. This button's primary function is to initiate a WhatsApp conversation. Currently, the button to chat with a seller is located at the top of the page and when users scroll to the bottom of the page, they need to scroll back to the top to initiate a conversation.

I'm including two links to convey my requirements. The first is my web app, the second is a web app that has implemented the floating button that stays at the bottom regardless of where you scroll to on the page. You need to view the links in mobile responsive mode.
- https://bit.ly/4gO3VKB
- https://bit.ly/4baMPWa

Key Requirements:
- Positioning: The button should be located at the bottom of the screen
- Display: The button needs to show both an icon and text.
- Design: The button should feature the WhatsApp logo with transparency

Ideal Skills and Experience:
- Proficiency in Front-end development in a NodeJS
- Ability to create responsive and interactive web elements.

Please let me know if you can help with this task.