You probably have cheap ass/free cell service like I do. Their servers don't like to comply. So use different ones. I had same problem. Finally got signed up on a solid wifi connection but then on phone I still couldn't send message (error) and Browse wouldn't refresh (error) and if I logged out I couldn't log back in (error). Then finally I saw a post somewhere about changing your APN to get better signal and voila! Go to Internet/network settings on your phone then click Mobile Network then scroll down and click Advanced then scroll down to Access Point Names and click it then click the 3 dot menu then click New APN and a form will come up with categories to fill in. The first category is Name and you put in "internet". Second category is APN and you put in "everywhere". Next scroll down to Username and you put in "eesecure". The next category is Password and you put in "secure". Don't fill out any other categories it will fill the ones that it needs automatically. Now go back to 3 dot menu and click it then click Save. Now click the empty dot next to your new APN to make it active. That's it. All done. Poof! All your problems with the app are gone.
Ps this will not screw up your phone or affect it working in any way
When you're not using the app you can go back and re-enable the original APN if you want or you can just leave it that way.
You're welcome.