Hello,
We apologize for the issue you are facing regarding tax exemption documentation for your upgrade from Rank Math Free to PRO. To handle your tax-exempt status, you can claim a refund after completing your purchase by contacting FastSpring’s consumer support. They will assist you in processing your tax exemption.
You can reach out to them through this link: FastSpring Consumer Support.
Additionally, if you want to add your VAT identification number during the checkout process, you can do so as shown in the image below:

If you have any further questions or need assistance, please reply to this ticket, and a human agent from our support team will take over and provide more help. Thank you for raising this concern!
Sources:
Why Does Rank Math Charge VAT/GST? » Rank Math
How to Get a VAT/GST Refund from Rank Math » Rank Math
Hello,
Thank you for contacting the support.
The rest of the amount above the price displayed on our website is added as a tax.
We do not have any control over that as that is charged by your government.
You can read more about the same here:
https://rankmath.com/kb/why-does-rank-math-charge-vat-and-gst/
If you have a valid tax ID (VAT, GST, etc.), then you can proceed with the payment and contact FastSpring (our payment processor) after completing the purchase to get a refund on your taxes:
https://fastspring.com/question-a-charge/#vat-tax-questions ( Request Tax or VAT Refund )
Hope that helps.
Thank you much. This is all for now. I appreciate your help!
Hello,
Glad that helped.
If you have any other concerns, please don’t hesitate to contact us anytime so we can assist you further.
Looking forward to helping you.