Hi Frank,

Thanks. We added donate button where the user can set the amount and can pay. https://dev.miusa.org/donate

in the free plugin, there are limited options. We have a pro version as well where we can create multiple forms and a lot of other options as well including subscription payments etc.

you can check here https://dev.miusa.org/wp-admin/admin.php?page=wpep-pro-features

If we buy it we can easily manage other book purchases etc as well using this plugin by creating multiple forms which are only possible in the pro version.

Without the plugin, I have tried creating an online checkout button however it seems due to permissions it do not allow me to create online checkout link for existing items.
https://squareup.com/dashboard/items/library/RMZVJE4LOXQAODRV55HSYZ5T
checkout screenshot as well.