@PERELLO Romain Thanks for posting in our Q&A. From your description, I know that you want to add a device identify in Corporate device identifiers in intune portal via Graph API. If there is anything misunderstanding, feel free to let us know.
For this issue, please make sure that the value of "importedDeviceIdentifier" is at least 14 numeric digits.
Then try again and check if the device identity is added in intune portal.
Hope it will help.
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