It looks like you're using stripe to process your payments. Does this mean that if I send a 1-character message it will cost you money?
( $10.000 / ( 0.3 + ( 0.029 * 0.01$ ) ) * 0.01 = $333,01
We would need a javascript script that would make 33301 payments of 1 cent.
This would be a very cost efficient attack between business rivals.
Perhaps if you spent less than 33 cents he won't...