Account Promotions Add-On; Account Type Promotion, Entering an overriding 'To Date' causes an 'Invalid' message to display

Creating an overriding First Payment on an Account Type Promotion may cause an error message to be displayed.

When entering an overriding First Payment period of 'On Date' or 'To Date' then clicking 'Next', a message was displayed advising the period was invalid.

ERROR MESSAGE
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Failed to validate Account Type Property Overrides.

First Payment Period invalid.