Supplier & does not exist

What causes this issue?

You have entered a supplier number that does not exist in the system.

How to fix this error?

Check your entry:
Does your entry correspond to the number on the invoice?
No --> Overwrite your entry.
Yes --> Check whether the supplier is recorded in the
system under a different number.
For this purpose, position the cursor on the
field <LS>Supplier</> and press F4 to generate a list
of all suppliers stored in the system:
Is the supplier recorded in the system under a different number?
Yes --> Choose the correct number from the list.
No --> Post the invoice to a one-time account or create
an account for this supplier.

Error message extract from SAP system. Copyright SAP SE.