Canalla translates to "scoundrel" or "rascal." It's a strong, somewhat old-fashioned word that adds a dramatic flair to the lyrics.
In the song, Morad uses it to describe someone who is thrown out for being unreliable or disloyal: "Y si apagado ya te echan por canalla" (And if it's off, they'll kick you out for being a scoundrel). This word highlights the harsh realities and codes of conduct in the environment he describes, making it a memorable and impactful choice.
Morad names the problem in his first line and then spends the rest of the track explaining where it came from. Sigo viviendo con mi paranoia (I keep living with my paranoia), and the verses that follow read like a rulebook from the La Florida blocks of L'Hospitalet, rattled off fast and with no punchlines. Keep your phone on, because si apagado ya te echan por canalla (if it is off, they write you off as a lowlife). Never leave a friend on the run. Keep your word even when listening to the wrong person costs you. He remembers being small and watching the older kids lift perfume bottles and se montaban rápido en un Dacia (jump fast into a Dacia), which is a very particular kind of glamour. Not a getaway car. A Dacia.
The hook is where he stops defending himself. No juzgo porque peco (I do not judge, because I sin too) is the whole moral position of the song in four words, and it arrives right after he describes greed as the thing que rompe el saco (that bursts the sack) and leaves you in jail with no tobacco. He is just as blunt about the fame: No soy famoso, nunca he hecho una firma (I am not famous, I have never signed an autograph). Then the outro hands the song over to a chant against the Catalan police, repeated until the beat runs out, which tells you how much of the paranoia he built himself and how much of it was handed to him.