You have to specify a valid date.

你必须指定一个有效的日期。

youdao

Value must be a valid date.

值必须是一个有效的日期。

youdao

Not a valid date.

不是一个有效的日期。

youdao

The band's website said tickets remained valid and a new date would be released within seven days.

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All tickets for Wednesday's gig will remain valid on the new date, although refunds will be given to fans who are unable to attend.

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The winner will be chosen from the valid entries after the closing date.

CNN: Terms and Conditions