“Ajax error while adding field” on Gravity Form Editor when adding “Mailchimp”

I’m trying to do the Mailchimp / Gravity Form integration by adding the “mailchimp” field on the form I need and keep getting this error “Ajax error while adding field”

I’ve tried to solve this by upping my PHP memory, switching permissions, logging out, clearing caches and different browsers but the problem persists.

I believe there is an error in the strace output

`write(4, “2018-01-31T21:17:40+00:00 CRITICAL Call to undefined function gf_apply_filters()\n\n”, 82) = 82
close(4) = 0
setitimer(ITIMER_PROF, {it_interval={0, 0}, it_value={0, 0}}, NULL) = 0
write(1, “Status: 500 Internal Server Error\r\n”, 35) = 35

But I’m not sure how to fix it. Might be a plugin developers job

Thank you!