All iOS in-app transactions are directly handled by Apple through iTunes, and unfortunately, we do not have any influence over what payment methods are accepted by Apple.

Please refer to this link to Apple Support site on how to 'Change and Remove Apple ID payment information': https://support.apple.com/en-us/HT201266

For more information on accepted purchasing methods, please refer to this link: https://support.apple.com/en-us/HT202631