Hi guys,
Elliot here – ACF dev.
Please note that the link field was added in ACF v5.6.0
@csk87 if you are using the free version of ACF (v4.x.x), this field type will not exist. Please consider trying ACF v5 in early access: https://www.advancedcustomfields.com/resources/beta-test-version-5/ or upgrade to ACF PRO: https://www.advancedcustomfields.com/pro/