There are a few taxi apps in Spain, one of them is MyTaxi (es.mytaxi.com). They all charge more or less the same as other apps, use the same fleet of official taxis, but the only difference is that this app offers an option to earn 1 Miles&More miles per 1 euro spend.

Another very attractive feature is regular 50% off sales which they hold for a couple of weeks every couple of months. this makes already cheap taxi rides in Spain – ridiculously cheap.
So I recommend having this app on your phone. When you register, you have to enter your payment details and on that page you will see an option to add your Miles&More number.
My understanding is that this still won’t prolong the lifetime of your M&M miles, which is 36 months. In order to do it you need to get M&M credit card.

10 euros off your first ride with MyTaxi

As other apps, MyTaxi is giving promo codes for your first ride: you will get 10 euros credit if you use promo code DmitryDro. In return I will get 10 euros too 🙂
After registration you will get your own promo code and will be able to share it with your friends, giving them 10 euros off their first trips and getting your 10 euros credit for it.

Please note that there will be no change given in case cost of your trip will be less than 10 euros. But since you can price your trip beforehand, you can use promocode in full.