Hey!
You do still need to get an ST Certificate under Delhi domicile as well from your nearest SDM. However, since that can sometimes end up taking a long time, for the time being you can go to a notary and get an affidavit made stating that you are eligible to be an ST candidate and that you have the caste certificate from your state ans that your Delhi certificate is under process. It will get the job done currently.
Feel free to ask further queries.
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