Through PayPal, you can pay with most major credit cards or directly from your bank balance, from almost anywhere in the world. You don't need to set up a PayPal account to pay with a credit card, and you don't need a credit card to set up a PayPal account.
If you don't already have a PayPal account, I recommend going first to the PayPal website and setting up your PayPal account before attempting to create a Project LRNJ account.
To be registered as a site member, you have to make a PayPal payment of $1 or more. Contributions under $10 (a Hi account) don't include any member version of Slime Forest Adventure, they just let you make an account and join the community with a username and optional profile.
The minimum to access the full kanji discrimination training in the web app is $1 (a Hi account).
The minimum to download the gradeschool kanji readings version of Slime Forest Adventure is $10 (an Intro account). The minimum to download the common use kanji version of Slime Forest Adventure is $20 (a Hat account), and this also gives access to the kanji readings training in the web app (which is still under development).
Additional contributions in any amount to help support development are gratefully accepted, and bonus material for higher registration levels is intended, though none is currently available and it can't be guaranteed.
All of your past contributions are added together to determine your registration level. So if you pay $1 to make a Hi account, and then a month later, you pay $9, you're upgraded to an Intro account, and so on. I reserve the option to make content available at lower contribution levels, especially if there are large numbers of small donations, but I will never take away content from an account that previously had access to it.
All old registrations are still valid, and some have been upgraded to reflect changes in the registration system. You can claim or recover control of your old registration on the member page, or if that doesn't work, I have full records of all transactions and if you contact me by email I can fix it manually.