How to send an email(text message) to phone number using SharePoint designer 2013 Workflow? firstname.lastname@example.org is working for SharePoint designer 2010 Workflow but not in 2013 Workflow?
Any other workaround would be helpful.
As a workaround, You can trigger a SharePoint 2010 Workflow from SharePoint 2013 workflow by doing the following:
Send Emailaction, try to add
Start a List workflowaction to start your SharePoint 2010 Workflow.
For more details check How to trigger a SharePoint 2010 workflow from a SharePoint 2013 workflow