We rent ours out but are in the UK but we have a keyholder (annual contract) who is registered to work in Spain. She also does the meet and greet and arranges the cleaning. If you only have a cleaner who is on call in the event of any problems when the renters are there? Who does the meet and greet/handover of keys?
On the contract we send to the renter they fill in their passport details, they are aware that these will be shared with the Guardia Civil and with the keyholder (GDPR requirement to disclose who the information will be shared with). We send the keyholder the details. Some keyholders will enter the details for you if you supply your log-in details, but the way we do it, (and 2 solicitors said this was acceptable), is she gets the guests to sign a hand completed copy of the form and then we enter the details on the Guardia Civil site and print that off. When we go to Spain she gives us the signed forms which we bring home and attach to the printed out ones that we completed.
Until you have your license it is still illegal to rent out short-term and you could still be fined. However you could do a mid-term rental (eg say 3 months) or long term without any need for a license, just contracts.