A Study To Assess the Safety of OnabotulinumtoxinA (BOTOX) Intramuscular Injection in Adult Participants With Platysma Prominence

Inclusion Criteria: \- Completion of all phases of the lead-in Phase 3 study (Screening Period, Treatment Period \[randomization/treatment with 4-month follow-up visit\] and Study Exit visit) Exclusion Criteria: * 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 * Tattoos, jewelry, or clothing that cannot be removed, and that obscure the target area of interest