Good morning @Jasmeen123 , a few questions for you. Have you been able to send texts to people before and this is new? Did you try using a different messaging app to see if that works? Is all outgoing texts or only to certain numbers?
Are you using the default messaging app that came on the phone if you can, try installing the Google Messages app and see if it works.
You can also try clearing the messenger app cache and see if if works. Go to settings->apps then look for the messenger app go into that and then storage and clear the app data and cache.
You can try contacting Fido by calling *611 on your device and have them reset your line.
If all fails try a factory reset.
Hope that helps, cheers