Based on common dropshipping advice and articles about Facebook Ads for beginners, the biggest mistake is often cited as:

Turning off ads too early or not having a sufficient budget/time for the Facebook algorithm's "Learning Phase" to optimize.

Beginners often get impatient, stop an ad after only a few days or dollars spent because they don't see immediate sales, and jump to a new ad or product, which prevents the algorithm from gathering enough data (typically around 50 conversions per week) to find the right audience and deliver the best results.

Other major, closely related mistakes include:

    Not properly installing or utilizing the Meta Pixel (which tracks actions on your Shopify store and feeds crucial data back to Facebook).

    Hitting the "Boost Post" button instead of creating a campaign with the proper objective (usually Conversions or Sales) in the Ads Manager.

    Targeting an audience that is too narrow (stifling the algorithm) or too broad (wasting money).

    Ignoring Ad Fatigue by running the same creative to the same audience for too long.