Rocking-Up-X-Mas-Gray-Cheetah Foundation The only other way I can come up with is to work with descriptions. You only have no hard control over it because the user can change that description.
With a link like https://bunq.me/RUX/0/Amersfoort or https://bunq.me/RUX/0/Zwolle etc you can specify the description.
You can also specify the amount, then you must replace the 0 with something else; you will get something like https://bunq.me/RUX/56,78/Amersfoort But both data can be adjusted by the user to something else, so it is not watertight.
In addition, you have to put someone on it who searches for all amounts from Amersfoort and who transfers it to the Amersfoort bank account, etc. You could possibly have it done by a program that reads the payments through the API and then transfers the payments to the correct bank accounts.
By the way, you can fix this if you first have such information entered via a website. Then you can (again via the API) have a specific payment request made with that data and the users cannot adjust the amount or description. If you then immediately make the payment request for the correct bank account, you do not have to transfer money from one bank account to the other afterwards.