If a SiteMinder reservation didn't sync to Guesty, check that the reservation originates from one of the supported booking channels and that the reservation has been imported into SiteMinder.
Check your SiteMinder reservation logs for any errors and reach out to SiteMinder Hotels Support for initial assistance. If Guesty needs to involved, contact us with a summary of the issue, any documented evidence you have, such as send logs, the response you got from SiteMinder Hotels Support, and your SiteMinder support case number.