Some templates require MIBs that dont ship with zabbix by default. In this example adding Unifi APs using this template requires the MIBs listed below:
FROGFOOT-RESOURCES-MIB, IANAifType-MIB , IF-MIB , SNMP-FRAMEWORK-MIB , SNMPv2-CONF. SNMPv2-MIB, SNMPv2-SMI, SNMPv2-TC, UBNT-MIB, UBNT-UniFi-MIB
These MIBs can be found and downloaded in txt form using a simple Google search.
Once downloaded, you need to copy the MIB txts to the zabbix host into a folder where MIBs are stored. By default this is /usr/share/snmp/mibs. After that you need to add the following line to the /etc/snmp/snmp.conf file:
#mibs :mibs +ALL
(Remove the mibs: line first, copy the whole line including the comment (#))
This will tell snmp to load all mibs in folders it is aware of. Then you're done, import the template and it should work.