Please ensure the organisation/group you have selected contains at least one repository.
In the case of GitHub make sure you have access to repository you are trying to connect. Access can also be restricted by configuring the Behave Pro app either in your GitHub organisation or account.
To learn more about Github repository access please see this article.
If you are trying to use GitLab, this depends on who completed the initial connection from Jira to GitLab. Behave Pro will be only able to access repositories that particular GitLab user has access to.
It is highly recommended that you create a machine user for this connection and give that user access to the repositories you want Behave Pro to have access to.
If you are using Bitbucket Cloud please make sure you are connected to correct workspace and that workspace has repository.
If you are using Bitbucket Server, you (your account) must have access to that repository in order for you to be able to select it.