Welcome to the community!
Are you still having issues sending messages? Have you verified that the phone has the correct SMS message centre (SMSC) number? It's possible the number might have gotten deleted following the update. The SMS message centre number for Fido is: (514) 993-1123 (see here and here). You should be able to find the SMSC under the messaging app's settings. For Samsung OneUI 3.1, Messages --> Settings --> More Settings --> Text Messages --> Message Centre. Other devices might have their menus organised slightly differently, but it should be similar.
Have you verified that the phone is using the proper APN? You can view the appropriate settings here.
Hope this helps 😀
Hope this helps