What the platform sends
The reportable set is your identifying details, including tax identification number and, for an entity, the business registration number, together with the total consideration paid or credited in each quarter and the fees, commissions or taxes the platform withheld.
Note "gross". The figure reported is what the guest paid, before the platform took its cut. Your books show the net you received. The two numbers are supposed to differ, and the difference is exactly the fees the platform also reports.
Why it may not concern you at all
DAC7 bites on platforms facilitating a relevant activity for consideration. A reservation platform that simply passes a table booking to you, taking no payment, is not obviously facilitating a paid transaction between you and the guest.
Where it does apply cleanly is ticketing, prepaid experiences, delivery marketplaces and short-term accommodation. If a platform holds the guest’s money before you see it, assume you are in scope.
The platform must also apply due diligence and can freeze payouts or close accounts for sellers who do not supply the required details, which is the usual reason a venue suddenly gets asked for its tax number.
What to do about it
Give accurate details when asked. A mismatch between what the platform reports and what your return declares is precisely what the exchange of information is designed to surface.
Reconcile gross to net once a quarter rather than at year end. Platforms report quarterly, and the reconciliation is much easier while you can still remember what a payout related to.
Ask any platform you sell through, in writing, whether it treats you as a reportable seller and what it has filed. You are entitled to know what has been reported about you.