how do i solve 412 Gmail_API: Invalid To header error

[ssenyondo67]

I keep getting the status code 412 response of Gmail_API: Invalid To header error if I send a message from my app.
but I receive a test email from the dashboard I can't understand why

[xr0master]

In this case, the error message describes the issue very well. The recipient address is not correct, it has to be an email address.

[ssenyondo67]

the error appears only when using the local host cause I have created a test project with the same code and deployed it on Vercel and it is working fine still am using the same details, it also worked on Fiddle shell
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