Persistent cookies not setting

Hello,
I just set up a registration form (gravity forms) within a popup with the goal of not showing the popup to people who have completed the form. I can get it to set a session cookie but not a persistent one, and only on popup close, not on form submission. In the meantime I included a close button.
I have tried deactivating all unrelated plugins to see if there is a conflict but no luck. I spoke with someone from my hosting provider, WPEngine, and they thought that setting something to not cache might help but uncaching the cookie itself did not fix the problem. Any ideas? I am happy to provide more information. Thank you!

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