Recart's Messenger feature and Shopify's Messenger Sales Channel works perfectly even on the same Facebook page. 

You don't have to turn off the entire Messenger sales channel, but you have to disable the Messenger updates on your Shopify Admin: 

You'll find the Messenger settings on your Shopify Admin - Messenger. Click Disable and now you can enable all Recart Messenger Campaigns - you won't send duplicated messages. 

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