Trying to populate non string value into a string for variable

Error Message

Trying to populate non string value into a string for variable ${opt:stage, self:provider.stage}. Please make sure the value of the property is a string.

Problem

Certain values in your serverless.yml are expected to take on a string type, but non-string values were assigned.

This usually happens when the value is a reference instead of a string, and the reference resolves to a non-string, ie. usually undefined or an object.

Solution

If you are using a referenced value, ensure that the reference can be resolved to a string.

For example, if you running into the error with the following reference: ${file(./config.yml):tableName.${self:opt.stage}}. Ensure the config.yml file exists, has the tableName attribute, and that tableName in turn has an attributte with the name of the stage you are trying to deploy to.