I guess that the reason why mine was corrected is that I am now able to use the UBER app and so my friend replaced my past tense with his present perfect tense.
Mine : Since I bought iPhone 4S, I can use the UBER app. Corrected sentence : Since I have bought iPhone 4S, I can use the UBER app.
Top answer
Your sentence is correct.
— Tamguatlay
Your sentence is correct.
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"Since you bought" is something that took place in the past. Hence, "bought" is correct. I think your friend used "since" in the sense of "because". To me, it is not appropriate.