Step 1 - Update your App
If you do not see a newer version, you can also join the Beta program here: https://trustwallet.com/beta. Please be advised that beta releases are experimental builds.
Step 2 - Confirm the Recipient Address
In order to send a coin or token, you need to have the correct recipient address. If the receiver provided the wrong address, the transaction will fail, or worst case your funds may get lost.
If you are sending BTC, make sure receiver provides a BTC address.
If you are sending ETH, make sure receiver provides an ETH address.
The token you are sending is in the correct type, ERC20, BEP2, TRC10/20.
Step 3 - Network Fees
As mentioned on the Sending Cryptocurrencies article, a small fee will always be required in one form or another before you can make transactions. Confirm if you have the necessary balance to pay for fees. This is always true for sending ERC20, BEP2, TRC10/20 tokens.
Read more about it here, Blockchains that Require Network fees.
Step 4 - Check Internet Connection
A stable internet connection is required. If you have a slow internet connection, this might result to errors or delays in submitting your transaction. Try switching to another connection or move closer to your WiFi hotspot. In some situations, enabling a VPN connection can also help. Make sure it is configured properly as it can sometimes block access.
Step 5 - Re-Import/Reinstall the App
Try doing a re-import of your wallet first. This will re-sync your wallet without reinstalling the entire app. If this still does not work, then completely uninstall the app, reboot your device and then start over. Download the app and restore your wallet.
Step 6 - Report the Issue
After doing the above steps and you are still unable to send, please get all pertinent data and submit a ticket. You can use this link to submit details of your concern: https://support.trustwallet.com/hc/en-us/requests/new