If that does not solve your problem then: Reinitialize the wallet. Please, before doing this, make sure you have your seed words available.. then Go to the terminal tab in the wallet and type: wallet init-seed –force It will prompt you for your seed words – after it loads, try again to send coins at this point.
If you get a message at this point saying “API authentication failed” then go to the about tab and click on Show SiaPrime Data which on Windows will place you on a path like: C:\Users\username\AppData\Roaming\SiaPrime-UI
At this point, close out of the wallet, including right clicking the icon on the task bar and quitting from there and then you want to rename the SiaPrime-UI folder to SiaPrime-UI-backup then open the wallet again. The wallet will re-sync and you will need to type in your seed words to open the wallet and should now be able to send coins.