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The number of Allowed Answer Choices for a List field is set on the Edit Contact Form page which the list exists on.
This means that if the same List Field exists on multiple Contact Forms, it can have a different Allowed Answer Choices setting on each form.
Steps
Go to the Edit Contact Form page of the Contact Form that features the List field
To the bottom right of the box that each field is in, press the number. By default it will say “1” to indicate that the Answer Choice setting is single choice
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Pressing the number causes the Allowed Answer Choices popup to load
It presents three options:
Single Choice
Limited multiple choice
Unlimited multiple choice
Select the option you want to use on that List Field.
If you have selected Limited multiple choice, you must enter a number between 1 and the number of Answer choices available on that list
Press save to close the popup
Scroll to the bottom of the Edit Contact Form page and press Save.
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Edit a List fieldManage your List fields