ERROR USING JOOLMLA USER SAVE ACTION

Please, I get ERROR 1048 (Column 'user_id' cannot be null) When I attempt to create USERS using the SAVE USER action.
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The USER is created but the group information is not included.
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Thanks for your swift action.

Just tested this, no problems here, please post a screenshot of your Save user settings.
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Best regards

Please, see the screenshot below:
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There you go, your group id provider is wrong. It needs to be an array of group IDs, and the syntax you've used is wrong. You'll want just {data:group} if it's an array, or if it's not use {data.split:group}

And it is not safe to get the groups ids from the data array, you should have a switch action, pass the {data:field_name} in the data provider, and set the expected value in the values box:

groupd_number:{value:[2]}