Tex. Gov't Code § 403.210

If a suit authorized by this subchapter is not brought in the manner or within the time required or if the suit is properly filed and results in a final determination that a tax or fee payment or a portion of a tax or fee payment made under protest, including the amount of interest credited on the payment, belongs to the state, the state retains the proper amount of the tax or fee payment and the proportionate share of the interest earned.