So, I had this issue while applying and I had already been approved for $900. When I was finishing my application on Straighttalk.com the website suddenly glitched and kept refreshing the page. I restarted my phone and re-did the application, only now it kept saying my application couldn't be processed at this time and I would get an email telling me to retry in 7 days. I just got off the phone with customer support and it seems what happened is that when the site I was trying to buy the phone on glitched it caused the smartpay system to think there was shady activity going on so it basically blacklisted me for 7 days. It's an identity protection failsafe. Unfortunately they can't fix or override it so all we can do is wait the 7 days from when it first declined your application and try again. Their website was also going through maintenance as well so if you were also having issues logging into your smartpay account that was why.
I hope this helps you understand what may have happened. It's an unfortunate inconvenience but that was the answer I recieved.
Seems all we can do is be patient and wait to re-apply.
If during that time you were using straighttalk.com and the phone you wanted sold out you can go to the other website StraighttalkSmartpay.com and they should have the phone you want in stock as well as in different colors and whatnot. The only difference between the sites is that StraighttalkSmartpay.com may have slightly higher prices then straighttalk.com. For example the Galaxy Note10+ is $899 on Straighttalk.com but is $1099 on StraighttalkSmartpay.com. So you should be careful and check the price of the phone and make sure it falls within the limit of the amount of your approval.