How to restrict to enter only negative amount for a specific expense type

Summary:

The expense type has been created to process refund of cash advances and need system to be restricted that only negative amount should be enterable for the expense type

Content (required):

The expense type has been created to process refund of cash advances and need system to be restricted that only negative amount should be enterable for the expense type

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Code Snippet (add any code snippets that support your topic, if applicable):