As an addition to my messages in the #general-plugins I've created this post as reference. Using two HDB PLAYER_HEAD as requirements as the format below doesn't work, it will check for one and accept the one ignoring the second item requirement.
left_click_requirement:
requirements:
has_item:
type: has item
material: PLAYER_HEAD
skull-texture: 54492
amount: 1
has_item2:
type: has item
material: PLAYER_HEAD
skull-texture: 68953
amount: 1
deny_commands:
- '[message] &cFAILED'
left_click_commands:
- '[message] &aAuthorised'