You do not have create authrorization for group &

What causes this issue?

In order to assign planning parameters to authorization group &V1&, you
must have create authorization for this group.

System Response

The authorization object for planning parameters is called G_820_GPL
and is made up of the authorization group and the activity, which has
the value 01 for create authorization.

How to fix this error?

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.