I recently updated my Lumia 930 to build 10581 form 8.1 and my messaging app is not working properly. I can not send text messages for some reason. Every time I try I get the message "Couldn't send". Is there a way to fix this bug?
There have been several people with this and many other bugs on this build, with most all bugs seeming to disappear after a hard reset of the device. Did you perform a hard reset after the update?
It could be that your APN settings have been messed up. The correct settings need to match what your carrier uses in order to work properly.
Not sure how to help further right now. I'll see if I can find someone else that knows this stuff. No promises, so you may want to do a search for the APN settings just in case.
Fwiw, I have a 930 with 10581 build and have had no issues with messaging whether it's SMS or Whatsapp. Likely the problem is on the cellular side in your case.