If the shares bought on T day are not short delivered by the seller, then you will receive a credit of funds on T+3 day for the BTST transaction performed on T+1 day.
If the shares bought on T day were actually short delivered by the seller, then the BTST transaction performed on T+1 day will go for auction settlement on T+3 day for which you receive an auction contract note indicating the auction buy price. And the shares bought on T day will be credited to your account on T+4 day.
Iām unsure how the CDSL sms is sent out but the above process is what actually happens.