You cannot define the sample for inspection type &1 manually

What causes this issue?

For inspection type &v1&, you want to enter the sample size manually in
the inspection lot. However, you have either set the "100% inspection"
indicator or have entered an inspection percentage or a sampling
procedure.

System Response

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

How to fix this error?

Cancel the "Manual sample" indicator.

Error message extract from SAP system. Copyright SAP SE.