Are there any limitations when it comes to receiving the signal on the device?
The goal of Sigfox is to create an ecosystem of low-cost long-lasting devices. The long-lasting part is important, because active listening (being able to receive a signal sent to the device all the time) would drain the battery much faster.
Because of this, Sigfox-based devices have to ask for the signal first and afterwards they are listening to the respective frequencies for some time (under a minute) - this is the time window in which they are able to receive the signal.
This means that if you want to change device settings via downlink (by sending the downlink sequence in a signal to the device), you need to first make the device request the downlink.
This can be done in several ways, you can read more about this in this article: https://simplehw.atlassian.net/wiki/spaces/DOC/pages/23396404/API+6+Downlink+Information