Lodger's identification document number for Spanish tax return?

[Mia143]

Hello,

I am a Supert host for a flat in Spain, My clienrs are very happy with me, but now they have found out that they have find out they have to pay taxes, 24% over the gross income, in other words it is not including their expenses, neither the cleaning or my fees.

How can they separate  the charges? so they pay over the net amount?

Have any other host had thie problem with American?

Thank you

Mary