Elsys Devices Downlink doesn't work

Hi everyone.
I have several types of Elsys devices that I want to change the device-config thought the Downlink , for example, the data transmission time can be increased from 10 minutes to 20 minutes.
I do this from this link Downlink generator – en (elsys.se)- SedndPer = 1200 , and I convert the Payload result to Based 64, and send it to the device as a Downlink on Chirpstack AS. But there is no change in the device configuration. Although it is confirmed.
Has anyone done this before?
Thank you