Welcome to the community. I agreed with @Nic Brough _Adaptavist_ stated. Another thing that you need to ensure is that the new field must already been added in your project's screen configuration scheme.
Best, Joseph Chung Yin
Jira/JSM Functional Lead, Global Infrastructure Applications Team
Team-managed project fields are independent of the global custom fields. Due to this, you will need to create the same custom fields again in the team managed project. Any system level (custom fields for company managed projects are not available for Team Managed projects)
There is an existing enhancement case with Atlassian to address this issue - https://jira.atlassian.com/browse/JSWCLOUD-20905
Hope this helps. If helped, please remember to click on Accept answer when you have a chance.