If any party to a contract does not have the ability to sue the other parties subject to that contract for their violations the contract is null and void.
The Eleventh Amendment prohibits a citizen of Texas from suing GA, PA, etc. But the Texas suit was brought by the State itself, not a citizen of that State. Thus, Article III, Section 2 is in full effect:
The judicial Power shall extend to all Cases, in Law and Equity, arising under this Constitution, the Laws of the United States, and Treaties made, or which shall be made, under their Authority;
--to all Cases affecting Ambassadors, other public Ministers and Consuls;
--to all Cases of admiralty and maritime Jurisdiction;
--to Controversies to which the United States shall be a Party;
--to Controversies between two or more States; . . .