You should pay tax on rental income from apartments you rent out, but you need to seek advice as to whether this has to be paid in your home country or in Cape Verde.
In Cape Verde there is a tax of 20% of income for renting out your property as at 2016.
In 2017 I was informed that if you live in Cape Verde and rent out a property you own, you only need pay 10% tax not 20%.
There is a form you should fill in for this purpose available from Finanza, which is also where you can make further enquiries.
Alternatively you can speak to your Management Agency.
There is also a Tourist Tax that is levied at hotels and resorts. LINK-TOURIST-TAX