Hello I'm happy its working for you, a few thoughts:
On the picture you have a pull down not a pull up(the resistor are from gnd not vcc) it will still work but if that is how you have it connected i would change
if (!digitalRead(buttonPin))
to
if (digitalRead(buttonPin))
to make sure it send on release and not on press, if you send on press then release interupt can mess with the transmission.
Another thing you should should have a lot more stable transmit, i tested the code and i miss only 1 message in 20, (7m distance)
Make sure the antenna lengths are correct and that you have all the caps you need(0.1uf and 10uf minimum)
Best of luck