On appeal, Drumm contends, inter alia, that the trial court erred in denying summary judgment because the Officers failed to meet their burden to show a waiver of the City's sovereign immunity. We agree.
"The doctrine of sovereign immunity, also known as governmental immunity, protects all levels of governments from legal action unless they have waived their immunity from suit." (Citation and punctuation omitted.) Watts , 294 Ga. App. at 862 (1), 670 S.E.2d 442. "The authority to waive the immunity of municipalities rests solely with the General Assembly and must be effected by statute." Id. ; see also Ga. Const. of 1983, Art. IX, Sec. II, Par. IX. "In the context of a contract action, ... sovereign immunity is waived only as to actions based upon written contracts." Watts , 294 Ga. App. at 863 (1), 670 S.E.2d 442. "An implied contract will not support a waiver of immunity under the provisions of the Georgia Constitution." (Citation and punctuation omitted.) Id.
"To constitute a valid contract, there must be parties able to contract, a consideration moving to the contract, the assent of the parties to the terms of the contract, and a subject matter upon which the contract can operate." OCGA § 13-3-1. "A contract is not complete and enforceable until there is a meeting of the minds as to all essential terms." (Citation and punctuation omitted.) Ga. Dept. of Community Health v. Data Inquiry , 313 Ga. App. 683, 685-686 (1) (a), 722 S.E.2d 403 (2012). "The burden was on [the Officers] to establish the existence of a written contract with the City and the resulting waiver." Watts , 294 Ga. App. at 863 (1), 670 S.E.2d 442.
In the absence of a written contract between the parties, the Officers argue that the text message exchange between Drumm and the Chief following their initial meeting where Drumm instructed the Chief to "[s]et up the paperwork" authorized the Chief to enter into a written contract on Drumm's behalf. To support their argument, the Officers cite to Art. 1, Sec. 5.10 (2) of the City's charter, which provides that the City manager shall appoint City employees and that "[h]e may authorize any administrative officer who is subject to his direction and supervision to exercise these powers with respect to subordinates in that officer's department..." The Officers assert that because the Chief was authorized by Drumm to enter into a contract with them, the letter from the Chief congratulating them on their promotion was an enforceable written contract.
Pretermitting whether the ambiguous text message exchange between the Chief and Drumm could be construed as an authorization by Drumm to enter into a contract with the Officers, the letter congratulating the Officers is not a written contract. "A contract cannot be enforced if its terms are incomplete, vague, indefinite or uncertain." (Citation and punctuation omitted.) Souza v. Berberian , 342 Ga. App. 165, 168 (1), 802 S.E.2d 401 (2017). The letter states: "Congratulations on your promotion [to corporal]. You have demonstrated exceptional qualities as a leader and we are proud of you. I wish you all the best in your new position." The letter does not contain any terms of the Officers' new employment and is too incomplete and indefinite to be an enforceable written contract. See Key v. Naylor, Inc. , 268 Ga. App. 419, 423 (1), 602 S.E.2d 192 (2004) (concluding that an alleged employment contract was unenforceable because it was indefinite regarding the employee's duties, term of employment, and salary).
*578Accordingly, because the Officers failed to meet their burden to prove the existence of a written contract, this action is barred by sovereign immunity. See Ga. Dept. of Labor v. RTT Assoc. , 299 Ga. 78, 82-87 (2), (3), 786 S.E.2d 840 (2016) ; see also Watts , 294 Ga. App. at 863-864 (1), 670 S.E.2d 442 ; Kennedy v. Ga. Dept. of Human Resources Child Support Enforcement , 286 Ga. App. 222, 224 (1), 648 S.E.2d 727 (2007).
Judgment reversed.
McFadden, P.J., and Ray, J., concur.