Just type a list of DOI with one DOI per line (and only this). Then click on « the launch check » button. A list should appear listing if the publication is uploaded to HAL. If it has an affiliation to the lab. And if so, the reference is given.
If a citation is entered more than once in the HAL database, a warning icon will appear and it will list all the refering entries in HAL.
As a reminder : it takes time for the database to be updated so if you just added an entry, the entry may still appear as missing. Check again the next day and everything should appear correctly.