Pre-defined amounts per campaign

Would it be possible to define different default/pre-existing amounts per campaign?

Yes. It is possible. You can :

1. Go to Joom Donation -> Configuration, find the config option Amount By Campaign, set it to Yes

2. Now, when you edit campaign , you will see a setting allows you to enter pre-defined amount (and predefined amount explanation) for that campaign

Regards,

Tuan