Step 1 - Determine 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.
Step 2 - Need Sufficient Balance for 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 tokens for ETH, BNB and TRX.
Step 3 - Signup to Beta Program
Always make sure you have a backup of your wallet. Join the Beta program here: https://trustwallet.com/beta. Once confirmed you will be able to get early releases of newer builds for your device. Check if the issue is resolved or if it still persist after installing the Beta app.
Step 4 - Test on Another Device
There are some cases that issue might just be with the device you are using. To further isolate, install Trust Wallet on another device and test. If this works then you might need to troubleshoot your own device further. Contact the phone manufacturer for support.
Step 5 - 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