Is there any REST API to fetch custom filed values based on project key, issuetype and customfield n

[Anitta Antony]

custom filed names are added to bug type screen GEN project made by me

[other surfing]

https://developer.atlassian.com/cloud/jira/platform/rest/v2/api-group-issues/#api-group-issues

Get issue

You can use ?fields=key, assignee, issuetype. Etc to only return those bits or the whole ticket. Other options available. 

You can do this in power automate, power query, postman and others.