There are multiple possibilities, Such as:

1. You have not enabled WhatsApp Chat in Shopify Admin theme settings.
2. You have not enabled WhatsApp Chat in application.
3. Check the availability time and timezone for Chat button and Support contacts.

1. If you have not enabled in Shopify Admin,

• Go to Shopify Admin
• In left side bar menu, find Sales channels > Online Store, Click on Themes
• In right side panel, you will find a Customize button for current live theme
• Then click on App Embed > Enable App Embed and Save as shown in image below

2. If you have not enabled yet in application,

• Enable it through the toggle button given in WhatsApp section,
• Choose the icon you want to show at storefront,
• Make sure its enable for Mobile and/or Desktop

as shown in the image below,

3. Check the availability time and timezone for Chat button and Support contacts.

Client on Edit Settings for WhatsApp Chat,

In Support Contacts section, 

Select “Available 24 hours” to make it visible forever

Or

Select particular timezone and From/To time

Click on Edit Icon (pencil) of support contact,

Change timezone and availability time for support contact & Save.

That’s it. You are done. WhatsApp chat widget should be visible now on your store.

Feel free to contact us and write us on our support email address, if in case you face any problem with app setup.