A Study To Assess the Safety and Effects of OnabotulinumtoxinA (BOTOX) Intramuscular Injection in Adult Participants With Moderate to Severe Platysma Prominence

* Participants must voluntarily sign and date an informed consent, approved by an independent ethics committee (IEC)/institutional review board (IRB), prior to the initiation of any screening or study specific procedures * Are willing and able to comply with procedures required in the protocol * Adult male or female, at least 18 years old at the time of signing the informed consent * Good health as determined by medical history, physical examination, vital signs, and investigator's judgment

* Any medical condition that may put the participant at increased medical risk with exposure to BOTOX, including diagnosed myasthenia gravis, Eaton-Lambert syndrome, amyotrophic lateral sclerosis, or any other condition that might interfere with neuromuscular function * Participant has an anticipated need for treatment with botulinum toxin of any serotype for any indication during the study (other than study intervention) * Anticipated need for surgery or overnight hospitalization during the study * Females who are pregnant or breastfeeding and are considering becoming pregnant or donating eggs during the study * Known immunization or hypersensitivity to any botulinum toxin serotype * History of clinically significant (per investigator's judgment) drug or alcohol abuse within the last 6 months * Lower facial and neck hair, scarring (e.g., acne), or other abnormal variations that may interfere with photography (such that photograph is not acceptable) * Tattoos, jewelry, or clothing that cannot be removed, and that obscure the target area of interest