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If the SIM you have currently selected doesn’t support text messaging or you don’t have enough credits to use text messaging on it, you can set the other SIM for the same purpose. On this screen, you can choose which SIM card can execute a certain action and you can customize it the way you choose.
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You can do so by opening the Settings app and going to Network and internet (labeled ‘Wireless and networks’ on some phones) > SIM cards (labeled ‘SIM manager’ on some phones). If that’s the case, you can solve the ‘Message not sent’ error by setting your currently active SIM as the default SIM for messaging. When there are two SIMs installed on your phone but only one is active (being billed for calls, data, and texts), that fact that you’re seeing the ‘Message not sent’ error displayed on the screen is most likely because your inactive SIM has been set as your default SIM for sending texts. Some Android phones have Dual SIM functionality that allows you to make phone calls and send texts depending on which SIM you choose to do it with. The most common reason for a failed text message could be the fact that you use multiple SIM cards.
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