Define KEY AIM
From SA-MP Wiki
To define KEY_AIM for use with GetPlayerKeys or OnPlayerKeyStateChange, place the following line directly under the inclusion of a_samp.inc:
#define KEY_AIM KEY_HANDBRAKE
To define KEY_AIM for use with GetPlayerKeys or OnPlayerKeyStateChange, place the following line directly under the inclusion of a_samp.inc:
#define KEY_AIM KEY_HANDBRAKE