The notifications are being sent too fast, our backend is getting overloaded with the simultaneous app opening requests. Can we somehow lower the speed?
Absolutely! You can do that from both Control Panel and Remote API.
First of all, please proceed to the "Send Push" form, then select "Scheduling" tab. Here you'll be able to see a tickbox called "Send rate". In the field below you'll be able to set the desired speed (measured in pushes/sec).
You'll need to use "send_rate" parameter in your /createMessage requests.
Valid values are from 100 to 1000 pushes/second.
However, please use throttling carefully, as it might take an extremely long time to send all pushes if you set a too low value.