Upgrade to plan which has lower price produces some problems and errors related to invoice and payment
Now I can create many instances of upgrade definitions to limit which are allowed upgrades
Unfortunatelly that means that for 10 plans I have to create 9 upgrade definitions
Doable but its would be easier if there would be an option to allow only higher or equal price upgrade
Why equal ?
Because it could happen that you can set addons which are not mandatory and later on customer will have possibility to upgrade plan only by buying addons