There are two types of data that, if missing or provided late at settlement, will lead to you paying more.

1. Airline addenda data 

2. Authorisation downgrades;

What can you do about it?

You can only fix it if you know it’s happening.  So, contact your PSP, gateway or acquirer and ask for a “qualification of downgrade report” (use those exact words!), particularly for any transactions involving North America.

Beware of the convenient solution.
Sometimes that means it’s costing you more. That may be fine with you, if convenience is what you want more than anything else, but is it worth it? Many providers will give airlines blended pricing, with everything in one (card brand fees, bank interchange fees and processor margins). It’s simpler, but then not as transparent about exactly what you’re paying and to whom.
 

What can you do about it?  

Firstly, ask your provider for a report that shows your pricing breakdown. Then see if your pricing is fair and competitive for your volume and the countries where you’re processing.

A number of airlines have not changed their locations or routed their transactions accordingly after Brexit. In some cases, you’ve still got EU cards settled in a UK location or vice versa. Before Brexit, those types of transactions would have been classed as intraregional, now they’re interregional – so you’ll be paying way more.
 

What can you do about it?

Review the routing of your transactions and locations post-Brexit.  Not all payment providers are able to support this re-routing if they don’t have cross-border capabilities, so check yours can.