What is the passport expiration requirement when applying for an eVisa for Thailand?

Be very careful if you hold British passport. The expiry date is 10 years after the issue date. Many countries do not recognise that last 6 months. So 10 years from the issue date.

Please correct me if that is wrong

Six months beyond your date of entry.

Now here we go if you want to just for 3months on an e-visa 6months after the leaving date ,not practical if you want it with a yearly extension at the least 1year and 6months clear

Upon arrival in Thailand