Full product & for item &, PO & not posted (partial quantity occurred)

What causes this issue?

Material &V1& for purchase order &V2& in item &V3& cannot be posted.
You tried to post using a unit that is different from the
<DS:GLOS.3526C0C9AFAB52B9E10000009B38F974>order unit</>.
You also tried to post a
<DS:GLOS.3526C180AFAB52B9E10000009B38F974>partial quantity</>, but the
system does not allow this.

System Response

The item mentioned above was not posted. The remaining items that did
not contain partial quantities for posting were posted correctly.

How to fix this error?

Enter the quantity in order units for the item that has not been posted.

Procedure for System Administrators

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.