The BRD app does not charge any fees to send a transaction. However, the cryptocurrency networks require a "transaction fee". The cost of this fee is not based on the amount you are sending, but is calculated against the traffic on the cryptocurrency network. It varies as the amount of transactions sent on the cryptocurrency network changes.
When sending a transaction, you need to make sure that you have enough funds in your wallet to cover the necessary transaction fee. Otherwise, an “Insufficient funds” error occurs.
When sending Bitcoin or Bitcoin Cash, fees are calculated by the amount of data attached to your transaction. On top of the amount being sent, this data will include information about where the funds came from and where it is being sent to.
If you are sending funds that came from several smaller transactions sent to your wallet, all of the information from those smaller transactions need to be referenced in the new transaction. This increases the data size of the new transaction and may cause the fee to be multiplied several times depending on how large the data size is. Sending a smaller transaction may help in this case. Also, if you receive small transactions regularly, you may want to arrange for larger and less frequent payments instead.