Legal Question in Criminal Law in Texas

You should check the laws of the state where the subpoena was issued. In Texas, a subpoena isn't good past a distance of 150 miles. In other words, you can't be compelled to travel 800 miles to come to a court hearing.

Actually, you can be subpoenaed to come to Texas even from another state. However, the prosecutors would have to file a special application and get a court order (as I recall) and make arrangements for your expenses. These expenses would not be paid until after the case finished and you submitted all your proof of expenses.

If you just receive a "regular" subpoena in the mail from a Texas prosecutor, then it is not legitimate.

If you are being subpoenaed from another state, then their rules would apply.