Manual:Purchasing a License for RouterOS - MikroTik Wiki
MikroTik RouterOS Level 4 (SWL4)
What is MikroTik RouterOS?
MikroTik ROUTEROS L4, 15 Days of Initial Config Support, WISP AP Level 4
How to Upgrade Mikrotik Licence 3 to L4 (w/ english subtittle) - YouTube
How to upgrade a Mikrotik routerOS license key using winbox
MIKROTIK RouterBOARD (RBcAP2nD) (License Level 4) - The source for WiFi products at best prices in Europe - wifi-stock.com
MIKROTIK RouterBOARD SXT 2 (RBSXT G 2HnD) (License Level 4) - The source for WiFi products at best prices in Europe - wifi-stock.com
Manual:License - MikroTik Wiki
Mikrotik CRS226-24G-2S+IN Review - You want one (or more)
Mikrotik SXT 6 2-PACK licensed 28dBi 5.9GHz to 6.4GHz frequency range BaseStation CPE PtP link
Manual:License - MikroTik Wiki
Amazon.com: Mikrotik SXT 6 equipped with RouterOS Level 4 license and 28 degree Dual Chain 16dBi antenna. Can be used as Base Station or CPE : Electronics