What should I do if my Thai Non-O visa application indicates an issue with the 'Middle Name' field?

You must enter your full name exactly as it appears in your passport, matching each field accordingly. Even if your local naming convention separates given name, middle name, and surname, do not fill it in according to your local format. Also, do not rely on the auto-fill system, as I once had my given name mistakenly pulled into the surname field. My visa application was once canceled because the given name and surname I entered did not match my passport. In addition, if you do not have a middle name, just leave it blank, the system will automatically insert a dash. By following this, I successfully obtained my visa.

Check your data entry carefully BEFORE you submit the application, <- especially where you scan the MRZ (data page) of your passport and it auto fills the information, you can edit the auto-fill part.

Remember a data entry error results in a cancellation of your application, you lose the money and you have to apply again

This comes up on the Thai consulate in Tokyo's website when you go to click to the eVisa portal, I wish it came up on EVERY website that linked to eVisa because many many MANY people have had their applications rejected because of data errors

N/A or the word none will suffice.

Just put in a ‘space’ or ‘full stop’ as computer systems needs to have something in that box

Maybe it means your maiden name if you have one. Ask tod Daniels.