Upgrade to V5 Licensing issue

I use V4 and intend to upgrade to V5. I have V4 on 2 systems. One is kept offline as a standby for the main system and is refreshed by periodic restores from the SQL DB backups of the main system. I understand that I need a single license for a single DB. Does keeping an offline system with a copy of the DB require me to have another license? I am running a single restaurant.

Can I upgrade my standby system first to V5 , take a DB backup from it and restore it on the main system and install SambaPOS V5 to bring up my main system? Will there be a licensing issue or a break due to it?

If you had only one licence you would need to clear the licence for the main database/machine and reactivate on the seccond machine when switching it to live use to avoid activation popups.
Many people will likely run a seccond database as a testing and development instance and put up with activation messages as it’s only testing/dev.
Does that make sense.
Depending on your setup two licence might be required if you want seamless switchover - ie if offline server has exact name/IP of main machine and you want to be able to just disconnect/shutdown main server and connect backup server. However even then I’m not sure how that will effect thelicence system and even then it may still need user interaction if client terminals know licence details and may get issues needing clear and activate to clear out client terminals lickence details.
If backup is different and you intend to change connection string you are making changes anyway so licence activation could just be part of procoess by definatly needed.