Ind. Code § 34-50-1-5

Sec. 5. An acceptance of a qualified settlement offer must be:

(1) unconditional;

(2) in writing;

(3) signed by the accepting recipient or the accepting recipient's attorney of record; and

(4) delivered:

(A) by registered or certified mail or by a means that verifies the date of receipt;

(B) to the offeror or the offeror's attorney of record; and

(C) not more than thirty (30) days after the recipient receives the qualified settlement offer.