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When I checked your e-mail address, the account that I found is in "Dormant" status. I activated your account again and checked your forms. There is no radio button at this form. However, I tried to achieve the thing you asked on my side. Unfortunately, there is no setting to limit character entered to the other option on the radio button. The only way to limit it is to make changes on the source code of the form, if you embed your form any website with source code embed method.
On the other hand, I am escalating this request to our Developers. This feather request will of course be considered by our developers but I can not promise you that it will be implemented right away or when it will be implemented.
If there will be any update regarding this subject, you will be notified via this thread.
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