Can you only use Amazon with vouchers?

I don’t know.

I had given my bank account for years and then paid for a while only with vouchers. Then someday, “please enter your bank account again.” That was suspicious to them, although (or because?) I had not bought as much in the period as before.

You can, however, if you add your bank account and don’t get Amazon suspicious – which sometimes leads to blocking, if you have sent too many things back – always enter a voucher code and only buy as much as it is on the voucher. I don’t know how this is at higher amounts. You can also buy vouchers worth up to 500€ in the supermarket. If you want to buy a larger electric device or something and redeem 2 500€ vouchers, I don’t know if Amazon is just going through this permanently.

The positive thing is, of course, that you have a better feeling for your expenses with the vouchers and can plan better if you, for example, charge a voucher and set a period of time in which this money must be enough for your purchases. Otherwise, a lot of “small stuff” comes together, where you can lose the overview.