text messages

I have 2 sim cards in my phone. The main one works fine. The second one....I can only call/receive call/receive a text message. The problem is I can't send any text message. It keeps writing: FAILED. It is bothering me. I called my operator but it seems to be fine from their side. I saw that...

Previously I was able to send a text message via Mi Cloud on the Web. However lately I noticed that the facility is gone. Is this a bug I have or is this feature gone? Thank you for taking the time to read, and help or information you can give.