Was the email still sent with "Portals:Send Invitation" action?(Screenshot below is the default one.)

If the default didn't work for you, it is easy to create a custom workflow as alternative:
Step 1: It is same to the default.
Use "Portals:Encode Invitation Code" action to encode original invitation code of invitation record.

Step 2: Instead of creating an email record and sending it with "Portals:Send Invitation" action,
we use "Send email: Create New Message" to send email directly.
Add the encoded invitation code from step 1 to email body.

Step 3: It is same to the default.
Change Invitation record status to Sent

Regards,
Clofly