Thanks for this, it's great! I will be implementing this in the future for sure.

I have one remark about the payment window... It would be great if we don't have to manually go to the @username/transfers page... 

For example if a user can fill in their own username once, then the payment page remembers this with a cookie... 

Then follow up visits can retrieve this cookie and offer a method to open the transfer window page without having to type it..
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