Hello Shivam !
Thank you for the quick response.
The custom field id created in functions.php. Here id the code screenshot. The field name is service_metatitle.

Then I added the custom field in the AIOSEO settings for the “service” taxonomy

The website interface is Russian, it;s convenient for you of course. The taxonomy slug is visible in the upper left corner. In the preview field we can see the website name (then we can suppose that nothing is added to the title.
I added some text to the service_metatitle field in one of the “service” taxonomy terms and checked the <title> tag in the head of the page. It was empty.
I can attach the screenshots of the edit page and the result page as well, both are in Russian and I think it will not help us to resolve the issue.