If you can't enable your migrate module due to already active configuration
This was my error message:
complinetmigration already exists in active configuration
This was the solution:
drush sqlq 'SELECT * FROM config WHERE name LIKE "%complinet%";' drush sqlq 'DELETE FROM config WHERE name LIKE "%complinet%";' drush sqlq 'DELETE FROM config WHERE name LIKE "%to_D8%";'