Audiences targeting issues - if you're using an audience that has outdated targeting (Facebook flags interests as no longer available) this can cause errors

Budget too low - when launching, the budget shown is in USD. We set the minimum budget possible - $1 / day / ad set - in USD. If your Facebook Ads Manager is in a different currency, you'll need to set the budget so that it is equal to 1 / day / ad set of your currency.

Lead form - when launching a Leads campaign, you need to make sure you've selected a Lead form or else the ads will not be created.

Facebook Pixel for Conversions campaigns - you must select a Facebook Pixel when using the Conversions Campaign Type or the ads will not be created.

Ads rejected - if your ads are rejected by Facebook for any reason you will get an error message in Marpipe.