Why am I unable to send pictures via text messages?

[EY310]

Security Warning and sending Pictures

I purchased an unlocked, used Galaxy s4 at Christmas. I've been receiving the warning, "security notice. Unauthorized actions have been detected." It gives me the options to restart or cancel. This appears several times per day and started a few days after receiving the phone.**************
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The other day, I was not receiving any texts. I was sending them and they** acted as of they went through. It wasn't until I found it strange that no one was returning my texts that I restarted my phone. I recieved a call saying that they've been texting me and I wasn't replying. I tried restarting again and it wasn't until the third restart that many text messages came through at the same time. I'm not sure if this is related to the security warning (above).
Also, I have not been able to send text pictures. I've tried to change the settings to make it the smallest possible and I continue to get the 'circle of death' that just spins and spins. My first day or two, I had no issues sending pictures.

Should I return my phone?

 

[Rukbat]

Re: Security Warning and sending Pictures

If you have the option of returning it, I would. You can find good used ones on Swappa running from $185 to $360 depending on carrier (unlocked doesn't mean all 4G bands) and condition.