Hi!
First stay in Thailand for 29 days then to Vietnam. Then back again after that to Thailand again. All the stay in Thailand will not be over 30 days. It that ok no problem just check in the airport and just show the ticket to Vietnam. Ticket turn return Thailand more than 60 days but going out to Vietnam inside of this periode.
Thanks for the advice.
TLDR : Answer Summary
A traveler plans to stay in Thailand for 29 days, then travel to Vietnam before returning to Thailand. They question whether this arrangement is permissible given that their total stay in Thailand will not exceed 30 days. Comments suggest that as long as proof of onward travel is provided (the ticket to Vietnam) and no extensive travel history exists, there shouldn't be any issues upon re-entry. It's also advised to carry proof of funds and accommodation for additional security upon entry.