The most common issue when facing this situation is that your Trustline has a set limit of zero or has not been activated.
To check and modify the limit of your SOLO Trustline, go to the Assets section on your Wallet and click on the “Edit” button, and modify the amount freely.
In case you have not activated your SOLO account it will show as “Not Activated” on the Assets window. The fee amount depends on the XRP Ledger fee at the moment. However, to make it easier for users of the SOLO DEX app, you can simply click on activate, and as long as you have more than 10 XRP your SOLO Wallet has been activated.