Amazon shows a ‘front end’ product page that is publicly available to buyers.  On that page there is a single Buy Box.  Your Offer is not guaranteed to be on that Buy Box and hence your price may not be showing.  Your Offer will be in the ‘from other sellers’ section.

Example: This merchant has a product that is $17.95 in their Shopify store, but wanted to list it on Amazon for $16.99.

You can see that the below Amazon listing is for $17.95 (which makes it appear as though sync isn’t working), but the Listing Seller does not correspond to the Shopify Seller's account. You can check the Amazon listing in question to see if you can find the offer they are referring to.

You can look for the Seller's name in the other offers and check to see if the pricing is accurate. In this case, it is! Just a matter of understanding the difference between a Listing and an Offer, and how to "win" the buy box!