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 (on mobile):
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