1. Install 0.3.7 (not 0.3.7 R2) from this link here
2. Disable your virus/malware scanner. For Windows 10 users, go to Windows Defender -> Virus and Threat Protection -> Turn off real-time protection.
3. Download and install SAMP CAC from lvcnr.net mainpage or here
4. Launch default samp.exe and play!
DO NOT:
Launch samp_launcher.exe. It will launch GTA:SA
Enable real-time protection after downloading. This will result in SAMP CAC not working!