The datetime string must match ISO 8601 format

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Posted on by marc756

"Unable to process template language expressions in action 'HTTP_Search_Time_Entries' inputs at line '0' and column '0': 'In function 'formatDateTime', the value provided for date time string '45930' was not valid. The datetime string must match ISO 8601 format.'."

I get the Error message because of a serial date format (45930) from Excels "getRows" connector despite having the advanced options set to "ISO8601". This occurrs since the start of this week, before this flow performed flawlessly. Nothing has been changed at the flow configuration.

Is that a bug currently in Power Automate? If yes it has to be fixed asap. My production flows rely on this.

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MS.Ragavendar 6,088 Super User 2026 Season 1 on at

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@marc756,

I am not sure this is know bug or issue in the system.

You can also try converting the values to ISO format using the addDays functions.

addDays('date', column, 'format')

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marc756 25 on at

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Here are my settings:

I would expect the date value from excel to be formatted as ISO 8601 respecting this setting. However, in the output the value remains in serial format:

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MS.Ragavendar 6,088 Super User 2026 Season 1 on at

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@marc756,

Kindly follow the below article which will solve your issue.

https://datamadness.medium.com/converting-excel-dates-in-power-automate-or-logic-apps-ac4cec40cbd1

✅ Please click Accept as solution if my post helped you solve your issue and help others who will face the similar issue in future.

❤️ Please consider giving it a Like, If the approach was useful in other ways.

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marc756 25 on at

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Thanks for the workaround. I just don’t see the whole point of setting the date format in the connector to ISO8601 if it still returns a serial date in the output . This clearly is a bug that needs to be fixed. Also because it used to work before.

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