'Unexpected character' error when adding a Process template with a 'Package' Type Parameter to a Project Template.

[Clare-Octopus]

Severity

Blocking customers from committing changes to a Project template with a process template that has a Package parameter.

Version

2026.3.10863

Latest Version

I could reproduce the problem in the latest build

What happened?

If I have a process template with these parameters, one being of the 'Package' type. (Note the package type is not showing as a variable value whereas the container feed type is):

And I then add that process template to a project template with these parameters:

I get an error when trying to select the project template values into the process template and commit the change:

Unexpected character encountered while parsing value: <value>. Path '', line 0, position 0.

Its possible the error relates to the fact we expect that package parameter value to be a variable and its showing as plain text. I did try changing the Project Parameter name to a variable and commit that but that does not seem to work:

Reproduction

1. Create a process template with a package parameter.
2. Create a project template with a package parameter.
3. Add the process template to the project template.
4. Add the projects template parameter value to the process template parameter value.
5. Try commit the change, see the error.

Error and Stacktrace

Unexpected character encountered while parsing value: #. Path '', line 0, position 0.

More Information

Initial customer ticket (internal) - https://octopuscd.zendesk.com/agent/tickets/218955
RnD (Internal) - https://octopusdeploy.slack.com/archives/CNHBHV2BX/p1786548896119909

Workaround

I cant see a workaround at the moment, trying to edit the project template name to a variable contructed name does not work as mentioned above. If you are trying to deploy a container image you can use the container feed type parameter option as that works fine. Its just the package type that produces the error.