Inquiry Submission By PKLM

I will be travelling in a couple of days to Cambodia from Chau Doc in Vietnam and plan to get an Ordinary Visa on arrival (not a tourist visa).

Can anyone advise if I need any supporting documents for an ordinary visa? My understanding was that I did not need additional docs for the initial visa and they would only be needed for subsequent extensions, but the ferry company is suggesting we will need a ?letter of introduction??

Would be grateful for any advice, thank you!