raise util.CommandError('Only a single head is supported. The '
alembic.util.CommandError: Only a single head is supported. The script directory has multiple heads (due to branching), which must be resolved by manually editing the revision files to form a linear sequence. Run alembic branches to see the pergence(s).

• When the flask blog is deployed to heroku, an error occurs after running the pus to heroku. It seems to be a problem with the git branch? Don't know how to solve it.

• I found a solution: this happens when you go back to a revision that is not the last and then create a new migration. Now you have two branches, which Alembic cannot handle. Look at how the migration files are chained together through migration ids, you need to create a linear chain to collapse the branches.

• I don’t quite understand. Don’t know how?

• Thank you very much.