If you plan on making certain products shoppable on Instagram, you will want to have your Facebook Shop catalog linked to your Instagram account. To complete this, follow step 4 in this article to link your Facebook Shop Catalog to your Instagram: https://business.instagram.com/a/shopping-setup-guide
Specifically,
To turn on product tags:
- Visit your Instagram business profile
- Tap the ellipsis (...) or gear icon in upper right hand corner
- Tap Shopping under Business Settings
- Tap Continue
- Select the product catalog you want to use with shopping on Instagram
- Tap Done
Related Reading
Setting up Facebook Marketplace: Common Questions and Answers
Best Practices for selling on Facebook