How do I find the Reference ID needed for registering on the ThailandPlus App with my COE code?

A user is inquiring about the Reference ID needed for the ThailandPlus App after obtaining their Certificate of Entry (COE) code, as their flight departs the next morning. Multiple community members respond, indicating that the Reference ID may not always be necessary, based on their experiences. Some mention it's a 5 or 6 digit number given by the embassy, while others suggest that it wasn't required during their travels, implying that users may not need to worry about it unless specifically asked during check-in or immigration.