Don't file your guests in the wrong place.

• The portal is the Mossos', not SESregistreviatgers.mossos.gencat.cat. Send your data to the national SES.Hospedajes and, as far as Catalonia is concerned, you've filed nothing.
• 24 hours from check-inEvery guest aged 14 or over, every stay. No grace for weekends, late flights, or a portal that's having a bad day.
• You need a Spanish or Catalan digital identityidCAT, idCAT Mòbil, Cl@ve or an FNMT certificate. No NIE, no credential — which is the wall most owners abroad hit first.
• Keep the file for three yearsIf you let regularly enough to count as a professional host — most Airbnb and Booking listings do.

Why Catalonia is its own island

Real Decreto 933/2021 sets the rules for all of Spain, but Catalonia has its own integral police force with full competence over public safety. Exercising that, the Generalitat runs the Registre de Viatgers dels Mossos d'Esquadra. The fields it wants look much like the national ones — name, date of birth, nationality, document, around twenty per guest — but the portal, the login and the procedure are all different. If you also manage a place in Madrid or Málaga, do not assume the process carries over. It doesn't.

The bit nobody mentions: the data you collect isn't identical for every guest. A Spanish national has a second surname and a document support number; a visitor from abroad gives a passport number and country of issue and leaves the second-surname field blank. And for guests who live in Spain, the file wants official province and municipality codes — the kind even the guest doesn't know off-hand. The required set shifts with where the guest lives, and a mismatched file simply gets bounced.

The real bottleneck: getting in the door

You don't log into the Mossos portal with a username and password — it needs strong electronic identification. For any accepted credential you need a valid NIE and, in practice, either a Spanish address or an in-person appointment. If you live abroad without one, you've got two roads: build your own credential (NIE first, then certificate or Cl@ve — months and a couple of trips), or appoint a representative who already has one and let them file on your behalf via a registered apoderament. Most foreign owners I know take the second road.

Cited, so you can check me

When guests arrive, they want the beach — not a form

Sitges in July: your guests have hauled cases from the station in the heat and they want a cold drink and the sea, not to stand in your hallway spelling out passport numbers. Doing the registry on the doorstep is miserable for everyone; skipping it quietly starts your 24-hour clock anyway. The trick is to take the form off the doorstep and let guests fill it in before they travel.

If you'd rather not wrestle the portal alone

More than one property, or living outside Spain, is exactly when the Catalan setup stops being a one-afternoon job. Stay Comply handles the part that genuinely hurts — collecting each guest's details in the right shape, resolving the official municipality codes, and producing a file the Mossos portal will accept. We're hosts who got tired of doing it by hand — and it's growing to handle tourist tax too. The final upload stays yours.