Everyone else is just telling you to do things in a way that is different, and while they are correct (you should use a unit.d/systems script for this depending on your distro), I’m going to actually answer your question since I know sometimes you just need a quick and simple way.
Depending on your version of cron, it may support special statements instead of the * * * * * notation for time.
The one you want is @reboot. Replace all entries of the schedule syntax with that, including the @, and the command will be executed only once when the system boots up.
Use that to start a script that checks for network connectivity on a loop with a sleep statement. Break the loop when you have connectivity, then execute your command, and exit the script.
Don’t ignore the correct way though. You’re better off executing this as a systemd (or equivalent) script. It’s barely more effort, and has the benefit of some nice built in logging and integrations.
Hey Op, since you appear to be somewhere in the EU based on your mention of Euro pricing, would you be willing to name and shame the wheelchair manufacturer and/or model?
Without giving too much of my own personal information away, I might be in a position to cause a bit of ruckus for this particular company in terms of bad PR, possibly legislatively. I work for a company that profiles itself on doing this stuff “the right way” (secure practises, not screwing users this way, etc) and we are working on building a list of practises we are hoping to root out EU-Wide with some examples that are clearly exploitative.
I need nothing personally identifiable, just the brand and model, and I can pass it along to the team that can investigate further.