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'Connection problem or invalid MMI code' indicates problem with the network (i.e poor signal) or wrong MMI code have being entered by the user. Otherwise, if user is trying to recharge through the mobile which has two active sim connections. Then, there is a chance for this error.
Sounds like you would need to get the same or very similar model Motorola E4 to do that. I do not know whether your cell phone service would need to be contacted to update the information.