I use this one. It will run level 2 if you ever have that setup in the future, but it comes with the adapter to run level 1, 110 standard US. Plus, it's 25' long, so you may not need an extension.
Keep in mind I don't know what you bought exactly. Maybe this? https://www.amazon.com/120-240V-Portable-Electric-Charging-Universal/dp/B07Y7HPKB6
For THAT model you'll need the usual 120V 20A outlet and circuit. But you claim you upvolted that to 240V so 15A is not a proper outlet and you risk fire along with the breaker tripping.
The model I linked to does not give any indication it will draw less than 16A on either 120 or 240V.
I own another model that allows for setting the Amperes such as https://www.amazon.com/120V-240V-Adjustable-Electric-Charging-Compatible/dp/B0BRT9L7C6 but I don't see an adapter for a 120V socket.
-> From what I can gather so far, you have the wrong 120V outlet (needs to be 20A.)
I second the Chinese Amazon chargers. I bought one like this: Book Engine Level 1+2 EV Charger(120-240V,16A,25ft) Portable EVSE Home Electric Vehicle Charging Station Universal https://www.amazon.com/dp/B07Y7HPKB6/ref=cm_sw_r_cp_api_fab_xDiIFbXHWRFPZ
It seems fairly well built and it’s been working fine for the year that I’ve had it. It comes with an adapter for your regular 120V outlet but it can also plug into a NEMA 6-20 receptacle for 240v charging which is how I’ve been using it.