By default, all SynapsePay fees are deducted from the fund recipient. This means that if you send $1, the fund recipient will get $1 minus the per transaction fee.
However, if you want your customer to receive 100% of the funds, you can cover the cost yourself.
Step 1: Pre-Fund a SYNAPSE-US Node
This is the node where the transaction fees will be deducted from. You will need to keep enough funds in it to cover all fees.
Step 2: During a transaction, set the facilitator fee to -0.20 (or whatever your per transaction fee is).
Also set your pre-funded SYNAPSE-US node as your fee's 'to' node.
Step 3: Check your response.
You will see two fees in the response. One one positive & one negative (corresponding with our SYNAPSE-US node & your SYNAPSE-US node respectively).
That's it! Your fund recipient should get 100% of the funds :)