Great question — answering as the UphillTech team:
I fixed this. I had received the following update from fast2sms You need to whitelist all URL (website links) which you're sending inside SMS on DLT Portal before 01/10/2024 else your SMS will fail. Watch this video: https://youtu.be/uajYj0bAM18 The video will give you more context. This is due to the new TRAI guidelines. I found Smler- https://app.smler.in . It provides custom headers, as its new, it seems to have good customer support if you run into any issues.
Full answer by Singh3y: https://stackoverflow.stackexchange.com/a/79043337 (CC BY-SA 4.0).
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