Unique index violation. Either fix the unique index so that new records can be inserted; or use different value for the unique index for the new record so that it will not violate the unique index while inserting to database. Check with your developer who can help you out.
This happens if you try to create a record with values of a unique index that already exist in another record. The solution is using unique values.
By the way, let me move this thread from the AX forum to a D365FO forum, because the screenshot clearly is from D365FO.
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