Income taxes (Details - Unrecognized tax benefits) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Unrecognized tax benefits, beginning balance	$ 0	$ 396,000
Additions based on tax positions of prior years	0	0
Reduction for tax positions of prior years	0	(396,000)
Unrecognized tax benefits, ending balance	$ 0	$ 0