How long can I wait before extending my Non-O visa if I'm short on income?

and this post isn't gonna get anywhere, because it's gonna come down to the immigration officer you're sitting in front of

Please note I am NOT being condescending or anything but medical malady, how much money you moved here to get surgeries, etc as a rule does NOT cut slack with the officers.

You either meet the requirements and you get the extension or you don't and you don't get it

Using monthly income method is spelled out clearly in the police order for extensions based on retirement.

You need to transfer in a minimum of 65k baht per month from abroad, each month, every month for the preceding 12 months to meet the requirements to get a year extension on monthly income.

From your post, you clearly didn't meet those requirements 😕

There's not a person on this group who is gonna tell you IF the officer will catch it or if they do catch it if they'll let it go. It's gonna take sitting in front of the officer and applying for the extension to find out.

I would go as soon as you can apply for the extension rather than wait until you're almost out of time, that way if you don't get the extension you have time to come up with another game plan.

You can go to your bank and get a credit advice, that shows where the transfer originated. But that's about it

I'd guess that June won't count as it stands but you should be able to go to the receiving bank in Thailand and ask them for an FET form for the £50 pound transfer

You can go to apply for your extension 30 days before your last day of the current stamp until that last day at most offices. But in your case, Maybe better to go to your local office as soon as possible to talk to them about your issue.

The police order is clear. It's "monthly income of no less than baht", not "around baht". Unfortunately, it has nothing to do with your extension application if you had this big amount transferred to Thailand before or not.

You need to contact wise and your bank to correct the record but it's out of the scope of this group.

If your record cannot be corrected, your choice might be to use the 800K baht banked money method.