Stuart uploads bank details to your Onsi account on your behalf. If you see an error when attempting to withdraw, it will be because the bank details provided for you are not valid. This could be a result of you entering your bank details incorrectly with Stuart or that Stuart has incorrectly added your bank details to your Onsi account.
We at Onsi aren't able to change your bank details, so please reach out to Stuart, advise them of the issue and ask that they update your Onsi account accordingly. Once they have done this then you will be able to make a withdrawal - please aware this may not be completed instantly (there may be a delay of up to 2 days).