I am transferring I-20 to my future university and they don’t accept my financial support letter because it does not say “the funds can be withdrawn at any given time”. Did anyone experience this problem or any tips?
You’ll have to get new financial support documents that meet the requirements of the institution.
US regulations demand that the funds for an F-1 student be “readily available” for the upcoming school year. That means you have to be able to get to the money at short notice.
If the money is sitting in a checking account in your name, it’s usually assumed that the money can be withdrawn and accessed at any time. If the money is parked in any other way (e.g. in an investment product or in someone else’s name), the college may want that stated explicitly.