Saving a Flow's JSON is different from publishing it to Meta. A saved draft does not prove that a customer can open it. Publication also depends on the supported number connection and the Flow access offered to that project.
Check the draft's validation and publication result. Linked-device numbers cannot upload Meta Flow assets; eligible Cloud numbers use the separate supported path. If publication fails, send support the Flow reference and redacted validation error. Do not send embedded tokens, customer submissions, or a complete private business form when a small example is sufficient.