Hi,
using
[email protected]
[email protected]
found a problem while deploying a state machine
	 IamRoleStateMachineExecution	Invalid principal in policy: "SERVICE":"states.${opt:region, self:custom.defaultRegion}.amazonaws.com" 
I'm a noob at nodejs but I managed to fix it doing in the serverless-step-functions/lib/deploy/stepFunctions/compileIamRole.js file :
- iamRoleStateMachineExecutionTemplate.replace('[region]', this.region) 
+ iamRoleStateMachineExecutionTemplate.replace('[region]', this.options.region) 
please see the attached patch
local_history.patch.txt
sorry for not submitting  PR, but I'm not sure if the fix is right :)
Regards and keep up with this good work!
Roberto