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I guess you'd like to accept only specific numbers on a number field you have. You can do this by using conditional logic. Please see this test form of mine:
Please see my condition on it:
If the number field is not equal to one of 1 or 2 "Name" field gets disabled and you can not submit the form since the field is required. There should be some other ways of doing this as well.
I hope this helps.
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