What a bummer! Thanks for your intent to donate; that, in itself, sets you apart from the masses. This is the support forum and, being volunteers, we cannot assist in this. BUT, you can contact the donation folks at https://www.thunderbird.net/en-US/donate/help/ and appeal to them to change their requirements. Thank you for sharing this.

For small amounts it may be denied due to their payment transaction costs.

https://www.thunderbird.net/en-US/donate/

What do the transaction costs cover? When you opt to cover our payment transaction costs, you're covering both our payment processing and donation platform fees. The costs associated with our robust online donation system allows us to continue scaling sustainably as our supporter-base grows. Our donation platform and payment processor partners reduce internal costs associated with maintaining our own system from scratch. Our partners ensure we can accept a wide range of currencies/payment methods and remain PCI compliant in all of the countries that we accept gifts from. The transaction costs you may choose to cover are based on an estimate of our overall costs. Due to many factors actual costs may fluctuate.

Are there additional fees added to my donation? We do not collect any additional fees or taxes. When you donate in your local currency you are not charged a conversion fee by your credit card. You can choose to also cover the payment processing transaction costs. This is completely voluntary and you may opt in or out using the checkbox on our donation form. Our organization is based in the United States. We encourage donors to research any additional external taxes or fees that may be applied by regulators such as your bank or tax authority.

@james, Thanks for sharing that. I never knew. Much appreciated.