BSNL data not working on phone

transferred the sim to another phone. calls and sms work but data doesnt.

its on sim slot 2

there could be a setting under sim settings for mobile data , it should be like a toggle. I use bsnl and 4G works well in certain areas but in few areas it goes back to stone age (2G)

BSNL internet, send an SMS with “START” to 1925 for mobile data.