Is it fine to share any promotional link in customer-seller messaging?

Yes, you can do that until it is on Amazon/on-site, you should never provide a link to your store on Shopify or something else.

It is not suggested

you can’t use Buyer-Seller Messaging for marketing or promotional purposes.

No, you cannot share any promotional link in customer-seller messaging

No, sharing promotional links in customer-seller messaging on Amazon is not allowed as it is against Amazon’s guidelines and policies.

Buyer-Seller Messaging cannot be used for advertising or promotion.

Sharing promotional links in customer-seller messaging is not permitted.

no you cannot share any kind of promotional link in customer-seller messaging.

no, don’t do this, it’ll create problems for you.