Hi Camilla,
This is Sanneke from Mews Support, nice to e-meet you!
Hopefully I can help you with displaying the voucher rates :)
There can be several reasons why not all rates are shown when the voucher code is added.
By default, Mews displays only one rate per rate group (the rate with the lowest price). So if the assigned rates to the voucher are all within one rate group, still only the lowest rate will be shown.
Therefore, if you would like to display different rates using the same voucher, they should be in different rate groups.
Please let me know if you have any additional questions!
Thank you @Sanneke.vandenBerg , moving rates to another rate group helped :)