Thanks for reaching out to Okadabooks.
The iOS refill option is system generated. This means that your account gets refilled with the equivalent you paid for after apple charges.
Apple charges a 30% and above commission rate on in-app transactions. Please reference the link below for details to see more details on this-https://www.bizjournals.com/milwaukee/news/2020/08/17/apple-app-store-commission-boon-headache.html
Warm Regards,
Ada